Hi Luis,

You'll need battens to extend the top of the main.
Don't use too heavy material highup in the mast.

I've used carbon fibre, split into smaller and thinner pieces, which I stuck on the sail with spinaker repair tape.

As carbon is very stiff, you can make it as thin as a hair and have very light stiff battens.

I sanded the battens smooth and conical, so they bend towards the mast and get stiffer towards the outer edge, helping to get the profile right.

Wear protective gear when working with carbon the way I described.

Regards, Jan.