Its no problem , I am the same age as you (13) but I have a non-erect about 5 inches and erect 10.2 inches (not to brag) and your girl friend shouldnt be afraid, just have sex really hard when she is not noticing and penetrate her and make her get an orgasm. Try putting her into 69 and keep pushing harder in and harder and dont listen to her your the boss. Once you got you're load dont let go then take out the dick put it in the garden's pusssy and push really deep in until you cant take it anymore then realese load in the valley. I have done this with my girlfriend and she doesnt mind. She gets often happy once she gets to have sex. MY girl friend is about 5.7 ft and has about 20DD boobs, she has a slender hairless body and she is 14, I am lucky she noticed my HORNY AS HELL DICK ON the bus at the back while sitting next to her. She started rubbing my dick then blowjobbing and licking it hard , luckily it was night and not much people were on the bus. Ok so dont let your girlfriend be afriad. Just penetrate her so she gets addicted>