Open Question: How much to start out with while bench pressing?

There's a bench press comp. coming up in a few weeks and only a few females have signed up. There's only one in my weight class though... Well, I am considering signing up but don't know how much to start out with. I weigh 102 lbs, 19 years old, and can pick up 120 lb. dumbbells using both arms (if that helps haha.) I don't know much about it, but would like to start training. Any help would be great!