Darling the only person you could possibly let down is yourself. You owe us on this forum, or other sex workers, nothing.
Consider this first booking a learning experience and adjust your profile and FAQs accordingly.
Does your profile say you will receive oral? If so, think about removing that if it's going to affect your performance.
Do you specifically say that you'll top clients? Do you feel that's realistic - are you going to be able to get hard if the client is unattractive? Obviously on this occasion you'd been drinking, which won't have helped.
Practise saying "No, I don't receive oral, you need to stop" and "I've already told you to stop doing X, if you try again I will end the booking."
Don't ever offer a customer a free session! Not unless you want a relationship with them. They will just come to expect a freebie every time.