Now you know what the re-sit options are, your best bet is to wait until Results Day, see what you get and then discuss with your chosen 6th form - or an alternative one - what they would let you do with the results you have. If you do re-sit in November then the results aren't out until January - you'll be lucky to be let on to a course on the assumption that you will get a better grade at that point, but there's no harm trying.