GIRLS!!! premature ....? please help :(?

okk well i am 14 years old and MALE, when me and my last girlfriend were making outt i had a HUGE , like the worst i have ever had.. and it was hard for like and hour because she was touching me and stuff.. (not like that) anyways when i stood up u could see pre Come through my pants.. about the size of a quarter... i was really embared and hoping to god she wouldnt see.. anyways what should i have done?! how do i prevent this from happening!? ugh :( sorry fer asking..