You have absolutely nothing to lose by asking them, I know someone who was allowed to defer as late as June (for Dentistry, so kinda similar).
It was down to the reasons for my doubts in the first place.
I was worried that the only reason I was going for medicine was because I'd convinced myself from such an early age that I wanted to be a doctor, and I wasn't really considering other paths. This wasn't helped when I went on a Cambridge open day, as I really liked the place, just didn't like the look of the Medicine course (as an option for me). I realised fairly soon that I still didn't want to do anything else though, so went for it