Let's just bypass the overall look of the board.
First problem. Foam selection. This type of extruded foam is really not suitable for surfboards. It will outgas and delaminate/shear rapidly. Secondly forget everything that you may have seen or read regarding open cell versus closed cell, because everyone seems to get it wrong. This is understandable as most board builders have very basic educations.
If you feel you can just sand it smooth through each step there really was no point in making a composite sandwich board. You should have just melted a bunch of plastics together and created a molded board. There is very little reason to add fiberglass if you are going to sand through it to smooth out bumps. Have fun, that fiberglass is going to get itching and once you heat that XPS up it will start to bubble.
Tape??? Why? This is not structural. You should have just used duct tape, at least it is reasonably porous and therefore with resin it could create a matrix. The epoxy has already started to dissolve the adhesive on the back of the tape, and in time the adhesive just deteriorates anyway. Additionally the top of the tape is coated and the epoxy does not adhere to the coating. Another shearing/delamination issues.
There is nothing craft about this. Building something completely wrong from the bottom up with the idea that the gel coat and paint will cover it up is baffling. It is like bondoing-up a rusted out car instead of properly fixing the sheet metal; or shim-shacking the framing for a house, because it will be covered up.
Properly cutting your fiberglass, with relatively clean edges, and good overlaps at corners will help. Additionally it is all about put resin on, letting it wet out, then squeeging a good portion of it out; this is particularly important around the rails.