[dr2005]

Provided your girlfriend has used the birth control properly (and the morning-after pill as advised), then you should be fine. While it is theoretically possible for sperm to be carried in pre-cum and result in pregnancy, the odds of it happening are very low so as Nicole said there is no need to worry too much. Had you ejaculated fully there would be a much greater risk, but in these circumstances it is very unlikely your girlfriend is pregnant. The main thing is to be more careful in future, and ensure you have stocked up on condoms beforehand in future. You should also make sure you use more than one method of birth control, such as a combination of condoms and the pill, so that you are covered in case anything goes wrong again in future.