Without wanting to sound rude to the people on here, the advice on the vet med forum is much more appropriate. There are people who re-apply 2,3,4,5+ times for vet med because there is nothing else they want to do. Vet schools are maybe more used to this than med schools, I don't know. But bear in mind that there is no funding for a graduate vet med degree whereas there is for a graduate med degree, and you have already said you can't afford to do a second degree.
I think you're panicking over not very much, you haven't applied yet. Just wait and see! You may be a tiny bit light on some areas of your WEX, but you can always improve on that if you have to take a gap year or book up the experience and tell them at interview that you have the experience booked up. Just apply and see what happens, if you get rejected then you won't be alone. Find out what was wrong, go away and improve it and come back even better next year. I'd suggest going back to the vet med forum, because as I said with no disrespect to the people on here, advising you to do a biological degree first is not really appropriate advice if you don't have the £45,000+ to pay the fees for your second degree.