hey, im 17 and have been seeing this girl for a few months now.

the past few weeks, we've spoke about sex alot. just via text, but i get really excited by this and get really hard.

the other day though, we tried to have sex, but i couldnt seem to get hard. i was being turned on but i just seemed to nervous, and in my mind i was scared because we always said how amazing sex was gonna be.. i just feel like i've let her down.

any help to improve my mental approach to sex? thanks.