['Hey! Yesterday, I signed for the gym near my house and an introductory personal training class with one of the trainers. Before leaving, I felt unsure if this was a good choice and what I should do.']
you will regret not going I think you should go
One time I just signed up for a gym and on the first days I was supposed to go, I signed up for a free lifting workout with the trainer there. Before I left I was wondering to myself if I should go or not, and wasn't too sure what was the best plan of action.