Problems getting an erection due to anxietyWatch
See a doctor if you need to.
Part of your mind going 'I don't want to do this really / I'm not sure I actually fancy her / She's a bit drunk... is she really ok with this? / etc etc etc' is a recipe for not getting hard. Especially if you're worried about not getting an erection.
Could you date / do other stuff before trying to do anything that needs one?