Six ounce cloth should be able to lay flat over most curves that are less sharp than the radius of an average pencil. I fiberglass paddle tips that are at least that sharp. A few tips:

First, definitely lay the cloth on a bias to the keel line, as Bill suggested. This makes the radius of fiber going over the keel less extreme. It also helps the whole cloth to stroke flat against the hull.

After wetting the cloth, revisit the keel every half hour or so through the 'sticky' phase and press down any bubbles with your finger. Eventually, they'll stick.

Kitchen wrap or other clear plastic can be laid over the wet fiberglass on the keel with a weight (small sand bags, damp folded towels, etc.) on top to hold the cloth against the keel.

That said, there is little reason to have such a sharp keel line on most boats. It will concentrate abrasion. Better to have a radius as big as an adults little finger.

John