Recently Had Sex How Can we be Safer?

Patient: My girlfriend just finished her period (about 9 days long) yesterday, and we had sex for the first time today. I wore a condom, and we stopped before either one of us climaxed. But when i was taking the condom off, I noticed some residue at the base of the condom. It looked like sperm (maybe precum?) but I’m not sure if it was. I know you can’t give an exact answer, but are the chances of her getting pregnant low? And is there anything more we should do to make sure she’s not? Also, do you have any tips for next time to be even more careful?