Thanks Colin!
Both you and chans formers suggested I should use Bondo... So yeah I picked up some and hot glue. I noticed the hot glue was super quick in filling in large gaps but messy as hell. I took scraps of styrene and stuffed it into the gap and hot glued it in. I then used bondo and the Tamiya putty to fill in the rest of the hole.
One thing I did notice was the Tamiya putty shrinks. So in future I'll need to build up the area and sand down when working with that stuff.