Ok, I managed to get the filleting done ok along the keel. I tried to make a long rounded tool to finish it all nice and neat, but it was too flexible and wouldnt push the epoxy down firmly enough. In the end I made the 'frosting bag' you referred to and squeezed the mixture in and I just reached in and smoothed it along with my finger (yes, I did wear gloves!). It was a bit messy but it worked better than anything else. I was able to smooth the edges with my fingers as well so the result was smoother than I was expecting.
The only thing was that when I was finishing near the point of the bow I was sqishing merrily away and I heard a crack. I think I might have been a bit aggressive and a tack cracked. After I took these shots, I inspected the top where the point of the bow meets, and it was just a bit loose, so I just gaffer taped it nice and firmly and it should be fine.
Then I went and cut the deck by tracing around the top onto the piece I had set aside for it. I wanted to wait until I had filleted just in case the shape was not exact, and as it turned out it was a bit 'fatter' at the nose of the bow, but not by much.
Now I am going to reinforce the deck section where I want to put bolts through for the spar fitting. I am going to glue a 10mm piece of ply to it, with holes drilled just big enough for the bolt heads to fit inside. Then I will push the bolts through and fill the recesses with epoxy glue to embed them nice and tight. I won't be able to get inside to tighten up bolts and things unless I make inspection ports, which I don't really want to do, so I need to make sure that the bolts are fixed for good.
Next is glassing the inside fillet. That will be fun. Actually I'm not concerned now that the fillets are done and fairly smooth.

This is the 'good' end.

Nice and square and symetrical.

Deck rough cut and ready for reinforcing.