Do not worry. You wine might still turn out OK, just a little thin. It is all part of the learning experience. I hate to tell you of all the disasters that have happened to me while I was just learning.
I would suggest that, if possible, you also give vinifera winegrapes a try. If you like the taste of concord wine, then I say "go for it", but if you want to try and make a wine in the style of a cabernet or merlot, then you need cabernet or merlot grapes.
I am not sure where you are exactly located, but the seems to be a huge number of companyies that sell winegrapes. It is not really too late in the season, you still might be able to get them.