You're fifteen, I can't even remember what school grade that puts you in. If my calculations are correct, it's 1998 and you're a sophomore at Valpo High. (I know no one calls it Valpo High yet, but in two years you'll be editor of the Viking Press and you'll begin using the name. It's not likely to catch on, though.)
I'm twenty five, by the way, so I've got ten years of wisdom on you. I don't want to tell you too much about the future, but you'll be slightly disappointed with some things in life, but you're really doing just fine and occasionally grateful for the things that didn't 'go right.'
I've been granted the opportunity to give you some advice, so I'll start with some specifics, and then finish with the psycho-babble.
Do pick the Viking Press over Honors pre-calculus. You'll have way more fun that way, but do not try to jump back up to the BC Calc class... you really aren't a math genius, and you don't like it anyway. (But, if you can't get the IB diploma without it, then take the plunge... not that the IB diploma will ever do you any good, but you're still awfully proud of it.)
When you're a senior, take a lot more than two days on your Princeton application, and for heaven's sake, don't apply to the engineering school. I suspect that well written essays, a few samples of Viking Press editorials, and an application to the Woodrow Wilson school of public service might actually get you in. The engineering route is a bad idea, and it won't get you into your ivy. Also, you shouldn't worry about the $50 - $100 application fees to the schools you really want to get in to. You're talking about thousands of dollars in tuition anyway, also might I suggest USC? It really is a beautiful campus. Finally, when you're still stuck choosing between Purdue and IU, pick IU's business school. You'll like it a lot more... and keep those grades up.
Other advice? Google at $87 is a bargain, 2003 is not the Cubs' year, but go to Atlanta anyway. Oh, and most all of the ballplayers who put up unbelievable numbers in the next few years are on steroids.
Now, for your life lesson, I'll briefly discuss friendship because it's the area of life that causes you the most stress over the next few years. The basic understanding you need to realize is that friends are made through concerted effort, not by meeting someone who just happens to be interested in the same things you are. In fact, most of your best friends don't really care about baseball, and certainly not the way you do.
One of your misconceptions about other people is centered around the concept of independence. You think it's a weakness to need or want other people's help? You're flat out wrong. People can see you're independent, but if you won't let them help you, they think you don't like them. If someone offers to help with something... they aren't just being polite, they really do want to help, and they're willing to spend time with you, which is an awfully good way of forming enduring friendships.
So, remember friendship is work, but it's awfully rewarding and you'll be way better off with good friends than you'd ever be otherwise, even if you somehow manage to get into Princeton (or USC).
The rest of life's lessons? I'll let you learn those in time. You're gonna have a hard enough time getting the friendship thing right anyhow.