A few things here: first of all congratulations for punting and having the confidence to go through with it.
Being nervous is very common, I still get nervous after punting for at least 5 years, I just embrace it. Don't use it as away of building confidence.
I think cutting any booking short is out of order, but at least you got 50 minutes, some men get kicked out after they cum once.
Obviously, I wasn't there so don't know hard you were, but maybe you weren't hard enough. I have fucked with a semi before and usually get harder inside her. To me it sounds like she didn't want it to run over time, rather than not fuck you, but did you say you wanted sex?
A good prossie would put the effort in and be able to get you hard again (maybe). Also, the prossie should listen to the punters request, so if you say slow down she should. I usually pull my cock out of her mouth in those situations. If it's any consolation I've had much worse punts than the one you mentioned here.