First time having sex!!!

Me and my boyfriend have a very limited time schedule, we have college every weekday and then both our parents usually stay at home on weekends. So on Thursdays we both have study periods last so we usually go back to his. We’ve been planning to have sex for a while and decided on today. Everything was going fine, he fingered me we were grinding on each other etc and then obviously we’ve never done it before so we’re both nervous and he gets out the condoms and his dick goes soft so I told him it was fine because obviously hes very nervous bless him. Then after we got dressed i had to catch my bus but we started making out and he got hard again? I know it’s down to nerves and limited time but I don’t know how to make him feel more relaxed :( Please give some advice!!