Advice for Getting into Universities

I'm only 15, heading into Gr10 this year, and I've suddenly been really worried about how I will get into university. I would consider myself 'smart', getting anywhere in the 90s for all my honors classes. With that said, I am definitely not a sport type of person, and am too shy to join one (although I am trying to work out and be more confident about this). I am going to finish Math 10 with 100% in summer school, and am going to finish math courses quickly, hoping to finish AP Calculus in gr11. This year, though, I only got into Science 10 Honors (and Math 10 Honors, but I am taking Math 11 Regular), due to some mistake which I do not know of because I do participate in class, teachers like me, and I have some of the highest marks, yet I did not get in.. I won't go into any further details about this, but yeah. Is that okay for me not doing honors? Also, I am trying to join clubs and things at school, but I have yet to decide. I basically need some general advice on what I should do so that after I finish high school, I can get into a good university. I don't exactly know what I'll be studying, so I am keeping my options open. I know this seems a little misplaced in a Maplestory forum, but heck, I was just curious and I know there are many adults here. Thanks for all the help.

Also, if I live in Canada, how would going to an American university work?

If you're applying to an American university, it should be the same process as if you lived in the United States. Just find the official website for the school and read up on their specific application processes, and how they may or may not be different for international students. But our universities love you, so I guarantee there shouldn't be any problem xD.

With regards to building a well-rounded, stand-out application, I would say make sure that, while high school GPA and standardized tests are extremely important and hold the most weight, the final deciding factors come down to who you are as a person and if you're the perfect fit for the university, so make sure you participate in various things accordingly. The best part about this is that it all comes down to what you like to do: join clubs, sports, activities, events, volunteer/leadership positions, etc., that fit YOUR interest and where you can truly excel. Similar to the search for true love, you should never design yourself to be a perfect fit for your dream school, if that design is not who you really are; your dream school is a place where you can thrive and excel as yourself. In the end, do your best academically while finding your niches in various places at school and in your community, participating and contributing to the success of everything you do. No matter what, have fun, get involved, and be yourself. Good luck!

Something I hear a lot is that you should focus on a couple activities you really like, instead of trying to be in 10 clubs at once. Like they want to see you enjoy doing whatever it is you enjoy, and you're dedicated to it.

Probably too early for this, but I think the essays are pretty important too. So you can practice those. Important for the university to see that you're a person, and not just listing all the things you did. I'm sure there's sample topics online, if not, I can dig out some I have. My best one was the prompt "describe an activity you do" and I did flyswatting and I was able to talk about how it needed dedication and patience and things, and people loved it.

Leadership positions really really look good.
So does volunteer work.

If I lived in Canada and wanted to go to an American University, would I have to do the SATs?

Depends on what area of the US you want.
South takes ACTs.

In general it just depends on which university you want to attend, which is again all discovered with research into your specific schools. But a lot of schools lately are taking both, especially in the Midwest and East coast.

EDIT: In response to above statement about the essays:

They're definitely very important, as they give the school a sense of who you are as a person, not just in the sense of how well you can write, but your character, personality, and history. To prepare for writing a good essay, my best recommendation would be to find out who you are, to the best of your ability. I knew myself very well Senior year when writing the essay, so I had no trouble with it, but looking back a year later I realize I didn't fully know who I was. Case in point? Don't worry about knowing who you are COMPLETELY, or coming to terms with everything, or whatever the case may be; the essay is not some deadline for you discovering yourself. Rather, take the time beforehand to do a little soul-searching so you can confidently write something from the heart.

what If I don't have a full diploma and did no extra activities?

Rather, take the time beforehand to do a little soul-searching so you can confidently write something from the heart.

Soul Searching = (human effort/2 - human suffering) + (success/2 - failure) + (experimentation - conformity) x ([(originality/4) + (product gains*4)] - common activities) + (practicality - philosophy) + (acceptance of personal flaws * (ability to cope with short-comings) - rejection of personal flaws)

* Note that if originality results in quantifiable above average product gain, then you can get rid of the "4" denominator.