Would anybody have any words of advice for me to improve for next time, if there is one?
Without knowing exactly why
you didn't make the cut it's almost impossible to answer, but I'll have a bit of a go.
From what the successful candidates have said here it looks like the older you the candidate was the broader the selectors expected your CV to be. Your options to do that whilst studying may be limited but if at University it wouldn't hurt to be involved in or better still even running one of the societies...if you're already doing that is there anything you can get involved with during vacations that might bulk your experience out?