How do I not think when I'm acting so I can loose myself when playing a character?

Gwen, I know where you are coming from because I too had that problem. There are a few things that you can do to help with that. One focus on what the other person is say. Listen to them and only them, know your scenes inside and out. Relax. And the biggest thing of all is to trust yourself, actors, and director. Know that you are not going to look stupid and no one is going to let you down. Don't worry about what you're doing, just perform. "Act well your part because there the honor lies" International Thespian Soceity.