When I glued the EPS blank there is a small gap between in the stringer and foam in certain places. Is it a serous issue?
The gap is no issue for strength of the board, the fiberglass shell is 90% of the strength after glassed. To make it look good you can squirt more glue into the gap and let it expand. If you have clamps then use them to pull the foam to the stringer and it will be 100% glued correctly.