Go over the hull thoroughly, filling any low spots including rivet holes, nail holes from scarf gluing, and missed spots in the laps with a sandable epoxy mixture. When it is cured, sand any high spots and repeat the filling and sanding process as much as you want. Remember, however, that your purpose is to have a boat to use, not to just to build one. Nick Schade, a kayak designer and builder, said in an article in "Sea Kayaker" magazine:
"When I build a boat I build it to use. A superfine finish is nice but can get in the way of hard use. If you have not built a boat before, consider your first project a learning experience. In the time it takes to build one "coffee-table" quality boat, you can build two very nice kayaks. The second will come out better than if you tried to produce a flawless boat the first time"
"Sea Kayaker" magazine Oct. 1995