Just a point about feathering.

Think of it as a scarf joint in the fiberglass. while the fiberglass is much thinner than a sheet of plywood, the concept is the same: TWO angled cuts overlapping one another and ending up smooth.

When doing a patch we first feather the edge of the existing fberglass, creating an extremely gentle ramp from the surface down to the existing wood. that eliminates any bumps or ridges. Let's say we make this ramp 2 inchws wide. At the middle of the "ramp" out glass cloth and resin from the original fiberglassing job is about 1/2 the desired thickness.

On top of this we apply a piece of glass cloth which is well saturated with resin. Once that resin hardens we sand over the patch, re fairing the surface, and removing any glass cloth or resin which is above the desired surface. In doing this you remove the glass which is above that ramp you cut, and effectively create another tapered edge from the glass and cloth which you apply.

Since you did not taper (or feather) the edge of the bottom layer of glass before you applied the second layer you are guaranteed to have a small bump.
Don't get too obsessed over it. If you try to sand down the overlapping piece you'll cut through it completely, and possibly go into the underlying layer. Try to cut through about half the thickness of trhe overlap. and put on a few extra "fill" coats of resin to smooth this a bit, and make it more fair.

And don;t ruh things. the glass and epoxy sand much better after you let them cure and rest for a few months. At the end of this season, or maybe next year, after you have banged around a bit and need to do some patching, treat this area to a patch, sanding off the ridged area and feathering the edges before laying on a new piece of fabric which connects the two pieces of glass cloth you've already applied. When you sand the patch fair your overlaps will be tapered and finally smooth.

hope this helps

PGJ