I am 18, and just had for the first time. but the problem is i couldnt really get hard as usual?

well it started at 11pm.i had to sneek into her house threw a window.by the way its a crank window and im 6'4 275.i never been that nervouse in my life.every noise in the house made me jump.but ya we had kinda but i couldnt feel anything,i couldnt get rock solid.idk was it nerves or is it bec im use to masturbating 3 time a day..idk help