Am I being blackmailed?

A little while ago my parents decided that they were going to make me sign a contract pretty much saying that I have to do all the chores in the house without complaining and that i can't ask my real dad or anyone for money to help me pay for a 1500$ school trip and that they wouldn't pay for it either. So they're practically making me do all the housework without time to get a real job or anymoney to pay for this trip. I tried asking, since they included my dad's name in the document to have him see it and approve of it; which i was denied, they then said i couldn't leave the room until i signed it so i had no other choice. Their reason is that despite the fact i'm an honor student, club leader and involved with a bunch of school activities, i'm lazy and need to start acting like an adult. If I don't, and break any of the rules in the contract then once i turn 18 they'll kick me out of the house. Right now with chores they're literally taking it as far as making me clean my stepbrothers piss off the floor, i don't know what to do! I love my parents and all, but they forced me to sign a contract that i can't back out of.