I can tell that you drew from that last line of instruction about drawing on past experiences but your first paragraph is so jarring and has relatively little to do with the rest. The connection between that line about the clash of intolerance and then at the end about the small classes creating a "tolerant and inspiring atmosphere" is there but it feels forced. I wouldn't mind so much except that first line is just so jarring and hits you in the face too much to not be commented on more. I would say to get rid of it if you want to keep the rest of it, which I think you do because that's what you chose to focus on. :) The rest isn't bad but it should all be related together.
Now I'm going to make a few changes. :)
The immense culture clash of intolerance crippled my excitement to meet new people and tomake my college a comfortable place to be .
Maybe say "and to feel comfortable in my college environment" or something.My thirst for knowledge kept me encouraged and enthusiastic to learn calculus, physics, and chemistry and to get closer to uncovering science's enticing mystery. After experiencing the disorienting 150-person lecture halls and competitive office hours, I realized even the academic environment Cal Poly offered was not conducive for me to learn.
If you can afford it, I think you should say why it was disorienting. I know it's because of the size but the size is something that some people might like so it could help to explain why it didn't work for you.
Err, never mind. You already did that in the next paragraph. ^_^
Macalester's offers small class sizes I will be comfortable asking questions, and its reputation of being progressive and accepting everyone creates the tolerant and inspiring atmosphere I will feel comfortable in .
I think you have to say "Macalester's small class sizes will allow me to be comfortable..." OR "Macalester offers small class sizes in which I can be comfortable..."
There is definitely an overuse of "comfortable." Find ways of showing that you'll be comfortable, not just saying it. :)
At Macalester, I have more opportunity ies to join those fighting for tolerance and change while simultaneously receiving a well-rounded education. At Macalester I can be the person I dream of.
The last sentence is nice but it's kind of out of place. I think unless you referred to earlier about looking up to certain people or wanting to be a certain type of person, you shouldn't include it. It's not substantial enough by itself to offer anything more to your supplement.
Good luck!