Am I really being stupid, or are people overreacting to my actions?

So today on the way to school, my mom wanted to know if we should go through the front or the back of the school, because she works there, I say front, because I don't want to walk around an entire school with Textbooks, a massive binder, my phone, a French Horn, and all my pencils, without a backpack. She literally said "My car doesn't want to go that far with us, either. She called me a wimp and went to the back. Then she asked why I leave my French Horn Case closed without the zipper, and the reason is, it gets stuck every time I open it, so I only use the Velcro. That has worked for me for two years. I'll admit I made a mistake when I loaded it on a Bus like that, and EVERYBODY makes it THEIR problem and yells at me, as if it's their French Horn their family scraped $2000 for. Also, I'm doing much better than I did last year with straight A's, and I'm not athletic at all. But in both, I'm always picked last for partners, when my friends say they'll finally pick me for once, and when I end up on that team, the people groan as if I did something to them that's terrible even though I have done nothing to them, and barely know them. What should I do about this?