Lower slump temp
You don’t provide a firing schedule, so this is just a guess, but I would start with lowering the top temp to avoid the “dog boning” as it is called, and increase the hold time to give the glass more time to settle into the mold.
Also, you should be fusing with at least two layers of glass to help avoid the sides pulling in. You can adjust the shape of the glass blank (making the sides convex to correct for the glass pulling in at the sides), but with the mold you describe, that should not be necessary.One adjustment could be to make the glass a little larger (1/4″) than the outside rim of the mold, which might help keep it from pulling in as much.
Jester’s Baubles Fused Glass Designs