I don't want to come off rude at all here, because what you've accomplished has been remarkable, but honestly what could have you expected would happen to your skin when you decided to cut big-weight FROM a 300+ pound frame?
Similar to an elastic your skin has been stretched so far, and held like that for so long, that it has essentially morphed into that shape, and will hold that form forever potentially. Of course a professional MD would have a much better option; but in my eyes, you would need surgery (maybe even a couple of rounds of it) to work on tightening lose skin around your chest/mid-section.
You've lost a lot and that's something to be proud about; but you got to realize getting back into shape and transforming your body is a slow process and can take years and years of work. I don't need to tell you that it was probably your life-style choices that created the original obesity issue; so that said, this time now and the years to come are the time to make up for the punishment your did to your body. And the time to put years back onto your life expectancy.
Good luck..
-VM