Am i big enough for her?

ok so be forewarned that this question is sexual. so i've been seeing this girl i really like in clubs and stuff and we dance and she grinds herself into my crotch. understandably, after about the third of fourth dance i start to get hard. i don't mean to be prideful or anything but when she ground into me the next dance, and she noticed i was hard she ran her rear the length of my penis. while i'm not the biggest (i just measured myself hard at about 7.5 inches long and about 6 inches around) she turned around and mouthed "wow". does she think i'm well-endowed or was she upset (she kept dancing with me even though i was hard and seemed to enjoy it)? is this considered big for a 20 year old? do you ladies actually care about size?