My condom slipped off when I pulled out

I had sex with my girlfriend last night. We used protection, I put the condom on properly and it stayed on pretty much all the time during intercourse as far as i could tell, but then I came, we waited a few seconds and when I pulled out, the condom wasn't there anymore. I panicked briefly, thinking it had slipped off sometimes earlier during intercourse and was on the mattress but then my girlfriend quickly pulled it out of her vagina; turns out it had apparently slipped off while I was pulling out, as I forgot to hold on tp the base of the condom when pulling out. My gf threw it away and told me it was full. I,m still a bit anxious though, is there anything to worry about? My gf dosen't seem to be worried at all, she told me she is very hard to impregnate and that she isn't in her ovulating days right now. She oughtta know as she was pregnant last year and sees her physician often. Still, should I be concerned? Is the condom coming off while pulling out a common occurance? Never happened to me before, that's why I'm concerned.