What do I do, Im in so much trouble :(?

Like said above, it's already taken place and you'll have to live with the consequences. Very little you can do now.=,=, It'd harsh they send a letter home, give you zeros, detention, and keep you from choosing your subjects. If caught at my school, all they do is give you a zero. It's possible to be written up for cheating and get detention or In School Suspension but not effect you from choosing your cles. Tell them that you had no patent or copyright protection on your work so allowing your friend to copy your work should not get you in trouble for plagiarism, because you didn't copy anyone's work without there permission. See if your teacher will let you redo the ignment.