Sex questions

Soooo I am sorry if this is a stupid question. I just started doing kegel exercises, just trying to strengthen my pelvic floor and to see what kind of differences in sex this makes. During sex, are you suppose to be “clenched” in your vaginal area like your doing an excerise or your flexing the area? I have never thought of it before, but normally during sex I am just relaxed and I am not flexing my vaginal area in any kind of way. Today I tried it, my boyfriend made a comment about how tight I was and he lasted about 20 seconds so I am debating if this is a good or bad thing now? Have I just been having sex wrong this whole time?