Are you using a male or female mold?

A female mold would be one you rent, buy, whatever. It will look like a
canoe shaped bath tub, and you pay your laminate inside of it (this is
how manufacturers build their boats).

A male mold is really more of a plug that looks like a slightly smaller
version of the canoe, and you drape layers of material over it. I've
seen a book called something like "build your own Kevlar canoe" and
they use this method. The results weren't something I would want, but
the boat appeared to float.

Gelcoat is air sensitive. If you are using a female mold, you can paint
or spray the gel into the mold, let it cure, and as long as you are
using a polyester or vinylester based resin it will etch into the gel
and bond. Epoxy will need a surface coat on the gel to bond.

If you are using a male mold, skip the gel. You would have to use
surfacing agent to let the gel cure (due to interaction with the air),
and even then it won't be very hard (the agent also makes repairs more
difficult). You could gel the inside of the canoe with a male mold, but
that wouldn't help with scratch protection or UV (the reasons to have
gel). The surface of a male mold built boat will be very rough, you
could possibly use house paint to give the boat color/ UV protection
without losing any performance.

The cost benefit of building a kevlar canoe is marginal at best. Unless
your time is worth less than $10 per hour, or you just really want the
project, it's better to buy one.

I'd suggest building a stripper before building a pure composite.
Strippers are made from cedar strips, and covered with a layer of
fiberglass.