I presume you are talking about the inside edges of the hull, where you are going to bond the wooden reinforcing strips to., rather than the deck edge.

Be careful not too take too much out, leave some "rough area" as it will help with the bonding of the 2 surfaces, make it to smooth and one slight knock against a bank and they might seperate.

HI Les
I suggest you carefully check the hull for the correct dimensions. Are you taking equal amounts off both sides of the hull centre line on the wood bits? if not then I would make a tracing of the hull on a large piece of paper ( wallpaper backing sheet), draw a center line and check for uniform spacing either side. I built a 48" Perkassa with a fibreglass hull many years ago and my hull was bowed on one side.
Good luck 😀

Thanks for the reply Dave. I understated the situation when I said I had to sand it down. I am having to saw and grind great lumps off to make the wood bits fit the hull

HI Les
Welcome to the world of kit building. 😊 in my experience most kits come with parts that need to be built up unglued and tried in place before final fitting.

Fibreglass hulls can and do become squashed in transport and wooden parts will allow for chamfering at the edges to allow close fitment to the hull.

You really need to check the hull to the plan before you start and make sure it is the correct width along the whole length, and has no overall twist from stem to stern. You can make temporary beams from scrap wood to push the hull to shape, or pull in the sides with string. I had a friend who used to use threaded rod (fitted thro' holes each side of the hull) with nuts either side of each hull side. By adjusting the nuts the hull can be pulled into correct shape.

You also need to check the top of the hull for correct depth to the keel, allowing for any rise at stem and stern.

Once you have an accurate hull you can build up the rest of the model adjusting any wooden or plastic fittings to fit.

Do remember that wood is from a living tree and can and will absorb or lose significant amounts of moisture. Storing the kit box in your work area with the lid off for a couple of days should allow the ply to adjust to your surroundings.

Good luck with the build 😀