I'm not familiar with the Parks brand, but normal epoxy (like West system, not 5-minute epoxy) starts to stiffen up and become harder to work with after about 30 minutes, though that does depend on room (garage) temperature. A full cure typically takes 24-48 hours, but it should tell you that in the instructions.

After the 24-48 hours, then you can sand it down (it's not that bad) and apply the first of a few coats of spar varnish. UV light will cause epoxy to turn milky with time, and you don't want that.

Forget the mold idea. If the epoxy starts to flow a bit after you apply it, you can just turn the paddle over to get it to flow the other way. It's only half an hour til it gets too viscous to flow, if that.

You might be able to get fibreglass cloth at HomeDepot or places like that, or try auto parts stores. Even Canadian Tire if you're desparate.

A couple of other suggestions:

Make sure you are wearing clothes that you are willing to trash if you get epoxy on them.

Don't take the safety instructions lightly, especially regarding eye protection. I have been told that flushing your eyes with acetone to get epoxy out is not fun.

If you're tempted to add more hardener than the directions say to get the epoxy to cure faster, don't. The 1:1 ratio (or whatever the directions say) needs to be followed exactly.

You probably have an inventory of stuff around the house that needs fixing with epoxy. Make a list and do them all at once with whatever epoxy is left over from the paddle.

Paddlemaker, I for one would be interested in benefiting from your knowledge and experience. Any chance of making some or all of your PM public?