How to be more mature?

I'm really sensitive :[ and im too scared to be my self at school because i thinki people are going to talk about me. I care TOOO much abotu what people think. im very self-conscious. i also hate my life and sometimes im suicidal. i hate it. im only 15 and im a sopho in high school. i can't forget the bad things that happened in the fast. some idiots well guys would say ewww when they see me even though im not fat or ugly i hope? please help i really need advice!!!!!!