Thanks for your letter to me
Having sex for the first time can often be an unpleasant experience. It's a new experience and both involved can feel awkward and uncomfortable.
As I don't know how old you are I will assume that you are both of the legal age (over 16) to engage in sexual activity?
As you have said in your letter you and your girfriend were both worried about pregnancy. Pulling out, otherwise known as the withdrawal method of contraception is placing your girlfriend at high risk of becoming pregnant.
Before you enter into any sexual relationship it's always worth finding out as much as you can about different forms of contraception that are available. Also it's important that you are aware of sexual health when sexually active.
Try having a look at some web sites that provide information and advice on contraception and sexual health www.fpa.co.uk or have a look at www.maketherightdecision.co.uk
Your girlfriend needs to keep a check of her monthly periods as there is always a risk whatever time within her cycle that she is likely to get pregnant.
If you have a close and good relationship talk to each other about what you want. It's important that you don't push each other into into doing something you don't want to do. And get information.
Take care and be safe
Sam