hmm, well - looks like either drop out of UCAS & reapply or try the graduate entry route (i.e. do maths & economics degree, then apply to a 4 year medicine course).
if you have financial concerns though - i think the GEP route may be even harder - not sure how it'll work in the future, but currently there's no guaranteed LEA support, so you pay full fees & i think are ineligible for a loan, plus the holidays may be too short to take on a holiday job & finally you'll already have the debt from your first degree! not to mention GEPs are incredibly competitive & your choice of degree may well limit where you can apply..
a longshot would be to try medicine / foundation year through clearing. though with maths & chemistry i wonder whether you'd be eligible for foundation courses.. but with the lcak of biology you limit the current medical schools you could apply to (check the thread at the top of this)
TBH, i'd be inclined to say withdraw from UCAS & apply for medicine next year if you're determined. i don't think the different financial situation will be that bad, given although there will be top up fees, there'll also be all sorts of new bursaries & funds! & the debt will still be less than the total you'd accumulate with 2 degrees.. plus in your GAP year you could save up some money.
but.. there is a risk you would have to take in that you might not get into medicine - so i'd want to make sure i absolutely maximised my chances - plenty of work experience & perhaps even take Biology.
hope these comments may provide some things for you to think about.. there are plenty of students on here who have gone the graduate route & some who've taken gap years to apply for medicine.. but none of us can really be absolutely certain about the financial situation yet..