How can i stop getting worried about getting my girlfriend getting pregnant?

Hi Polishbazooka, 

If she is taking birth control pills and she takes them exactly as directed then you really shouldn't worry about her getting pregnant. However, it is always a good idea to use a backup method if children are really not in your near future. A condom as a back up source is ideal because not only will it protect against pregnancy but it will also protect both of you from any possible Sexually Transmitted Diseases. 

If the anxiety persists, then you may have to reconsider abstinence if you are both very young. 

Best of luck,

Rosa