Before I really knew any of the intracacies of gel coat I did some small patches similar to what your tried. My hull was already old and spiderwebbed so I really did not care about matching the exact color so I did not try. I also did not widen out the cracks and used a fully pigmented 'white' gelcoat that was actually a pretty good match from > 20' away.
I'm kinda' with geehaw and others on this and I think that you did not add enough pigment to the 'matching kit' so the under layer colors bled through.
I'd start with a new can/container of fully white pigmented gelcoat and use your pigments on that.
The trick with pigmenting an already white pigmented gelcoat is that you take some white resin and you can put it on your hull (as long as no hardener has been added). Then you can mix in a few pigments to try to approximate the color (this done right on the hull). If the sun is directly overhead there may be too much light so morning or afternoon may give the best light to actually see if the colors are matched.
Once you have matched the color of the resin you mix in the hardener and apply. Gelcoat that has no hardener added should easily scrape or wipe off with just your friend Acetone.
Of course you can also mix up your tinted gelcoat on another surface such as a piece of plexiglass, glass or even cardboard but if it is right on the hull you can more easily see the differences in shades without any intervening borders that might distract your eye.
Be aware that most gel coat formulas require covering from air, as you did, but some are intended for over coating and are cured aerobically.
I took a marine survey course to pick up some of these details.
Good for you for trying. You make me seem very lazy 'cause I have plenty of divots like that in my 1967 Tartan 27' which I will (eventually) use a fully pigmented white gel coat on. I think I have a can of this stuff in the trunk of my car waiting to be used: Evercoat Premium Gel-Kote
I'll probably need some new MEK (methyl ethyl ketone - woo hoo!) to use as a hardening agent but at least I have the resin.
Ain't boat ownership grand?
Reminds me of the saying: "Life is what happens when you are making other plans."