A wee update on this.
I used a dremel to carefully grind away the gelcoat where it was cracked. To my surprise, the area underneath was sound. So all I have done is replace the gelcoat with plastic padding gelcoat filler. I have just used white filler so it is quite obvious where the repair runs into the yellow waterline, but it should be perfectly functional to get me on the water. Maybe at a later date I will try to colour-match a paint to hide this.
Good forecast for Saturday which is when I hope to finally get the boat launched. Still have to cut the slot in the centreboard and make up a retainer, but otherwise all good to go. I’ve been really pleased with how some of the minor dings and chips have come up with a bit of filling and sanding.