This might me a dumb question but I just pumped for the first time. I got 3oz. I have it in one of…

This might me a dumb question but I just pumped for the first time. I got 3oz. I have it in one of those insulated bag things that my diaper bag came in.. If I pump later can I keep pumping into the same bottle with the milk I already pumped or should I put it in her bottle and clean it and use a clean one for the next session?