Tell your parents your true situation. They won't be happy but you'll not have to lie and hold the truth from them. That alone can weigh heavily on your mind.
Choose classes that you can be successful in. That would mean delaying the physics class until later.
Get involved in a study group for each of your classes. You'll learn the subject better, make friends and actually have some fun while studying.
Make use of the professor's office time to ask for help.
Manage your time, school comes first. That doesn't mean no fun time, just work before play.