nervous scare

Can my girlfriend be pregnant if we had sex 18 days ago for the first time? We used a condom with spermicide. It lasted about an hour, but we didn’t know what we were doing, so I’d say there was only a total of about ten minutes of actual penetration, spread throughout the hour rather than all at once. I didn’t finish at all, and I did the water test afterward there was nothing wrong with the condom. She got her period, but it’s now day ten of bleeding, and it’s light brown blood with a light flow. I am very scared she isnt tho, she is nervous it might be something else.