How do I get my mom to back off?

First of all I'm 20 years old not a child like she seems to think but anyway she's always tried to boss me around but now she's going to the extremes since I'm gong to drop out of college so I can go to New York with my boyfriend who is graduating college in May and going to law school at NYU so I figured that this is my chance to go there and try to be an actress which is what I wanted to do after I graduated from high school but she made me go to college and the thing is I'm not even doing that well in school. I'm on academic probation and plus this is like almost the end of my 2nd year here but I'm still considered a freshman, that's how bad I'm doing but she doesn't get that and just feels I need to try harder and go to summer school since if I do that I will be able to graduate from the junior college I go to next May. She keeps going on and on about how going to New York is a bad idea and she won't support me financially anymore if I do go but I'm not really expecting anything for her since my boyfriend says he will be happy to help me out until I start getting acting jobs. All my mom keeps saying is that I'm dreaming so she doesn't support what I want to do at all! I'm so sick of her lecturing and bugging me about my decision and I have to deal with her until I leave in August. How do I get her to leave me alone?