I know you probably already know this, but I'm trans and I have a few tips :D
-You can use your beanie to make it look like short hair, you could do it at school too
-tanktops + tight sports bras = temporary binder . Please don't wear this every day though because it's really dangerous so be careful but this definitely helped me, then again I'm like medium sized chested so idk . This got me through 7th grade lol
-you can ask your teachers to use your preferred pronouns and preferred name , and request not to use them in front of your parents. Idk if it's like that for every school, but a lot of my friends do that .
Don't beat yourself up. You didn't choose this. And one day , you're going to be the man you want to be. The man you are <3
I hope you have a good day and good luck