The gap you have may not be as bad as you think.
Don't forget the covering material needs a place to go.
I leave a 1/32" gap all around when covering with film,
and a 1/16" gap all around when using fabric covering.
Don't forget the point of having a hatch is acess, I forgot
once and when I was all done I had to pound it in place,
and was a real bugger to get back off when I wanted to.

Good luck
Ralph V

P.S.
Paint also needs a place to go.