I reckon as you say just drawing a line under it and carrying on with the rest of the week is the best option. It sounds like you had a great day and every now and then that's more important than sticking to plan. And its not like there are many days in this country to enjoy beer gardens is it?
Great day planned for today to get back on track.
Have you got your date to go back to work yet? Are you looking forward to it or feeling a bit apprehensive? At least you have joining the gym you found to look forward to when you go back.