Do it. It will be a blast.
As others said, you don't have to worry about pushing yourself out. I don't remember how I even left the plane on my first tandem. The instructor will get you out.
I did have to do certain things on my first - body position and arching, altitude checks and pulling my own parachute.
This scared the hell out of me, becuase I had planed on getting so scared and passing out and having the instructor save my life.
I did forget everything for the second I was staring out the airplane, but a second after freefall started, I started calming down and remembered everything...and it was amaaazing....and it was supposed to be a one time thing, and here I sit on a skydiving forum counting down the days til my next jump.
So, again, do it! Even if you hate it (you won't), you'll feel so great about overcoming such a great fear.