You make it rectangle and while still too heavy, you round the corners. Then you only scratch off the last half belly millimeter to get 2 pounds above the target weight, then sandpaper it, shoot it 100x, make final tiller adjustments and finish the wood.
If design is long/wide enough and wood lines are ok, you do not need to back the hard maple. My experience is, maple can withstand more line violation that ash.
For 50lb poundage stiff handle flat bow make it 2 inch wide and 66 inch long. For such a eastern woodland D-design bending through the handle, effective length of working limbs is longer so you can make it a bit narrower, like 1 1/2 inch in the mid-limb. It will work with maple, elm, hickory or ash.