Being you have a riveted hull, I would suggest you invest in an air hammer, rivet tool and appropriate size solid rivets. It'll come in handy down the road. Being that the rivet in question is not only below the water line, but on the keel of the boat where it's going to get banged up eventually, I personally would feel more comfortable with a properly replaced solid rivet. It's not hard to do at all. I purchased a $12 air chisel from Harbor Freight, a brazier head rivet tool from somewhere online (brazier was the stock style of rivet on my boat, yours may be different) and I already had an air compressor. Total cost for a solid rivet replacement setup was around $25-30, including rivets. You'll need the correct size rivet for the stock rivet holes in your boat, also get the next size up for any rivet holes that are wallowed out during removal. This way you can drill the rivet hole to the next size and use the bigger rivet. Just my opinion, of course, but I feel much better knowing rivets I had to replace in by boat, especially below the water line, were replaced with properly set solid rivets.
Harbor Freight Chisel
https://www.harborfreight.com/medium-barrel-air-hammer-with-chisel-69866.html