DDs UCAT was not great, so she made an early decision to only apply for medical schools which she both wanted to go to, and which were likely to consider her, and to plan for a gap year, probably adding BMAT to the mix. (She is very dyslexic so not good at timed tests, which is also an issue for others whose slow processing speeds are down to having English as a second language etc.)
The main thing was to get good A level grades, so the focus was on gap year planning. If she had had to reapply she would have gained from the experience of applying first time round, would have been a year older/more mature and would have had grades in hand.
In the end she got three interviews (KCL, Birmingham and Bristol) and two offers. (She got in the last year Bristol did not use aptitude tests. Given that at the time they had 17 applicants to a place it is not surprising they switched.) By then, and all three of her interviews were in March, DD was quite attached to the idea of a gap year, so she asked to defer and was lucky enough to be able to.
Not getting a good score is pretty devastating as you feel you are starting a difficult process with your hands tied behind your back. Two other medical school applicants at DDs school were in a similar position and by March the three were hanging out together in the sixth form common trying to ignore excited talk of Universities, accommodation and others plans. Both were the first to congratulate DD when she got an offer, even though they both ended up without anything. One then got a (single) offer the following year, but one is enough and she went on to be at the top of her year. The other also took a gap year with the intention of reapplying and took a gap year job with a media company where he did extraordinarily well. So well that the firm offered a bribe for him to stay on and skip University altogether and for him to realise that even if his father was a successful doctor, medicine was not for him.
UCAT is miserable, but overall getting the grades is more important. It is worth trying to block the rest out and focus on these.