Do you know for sure it's wet? Does it weigh properly?
Stand it up vertically in the garage for a month and see what comes out the drain port. If you must stand it up outside (harder to inspect, but 14 foot ceilings are hard to come by), then cover it well to insure no water intake during the test. Put a cup under the port and inspect daily. 1 gallon = 6 pounds, give or take.
Standing a Sunfish up on end won't do any good - the drain plug is by the splashrail. If the boat is over 135 or so after being drained, some water is absorbed into the foam blocks. If you don't want to race, you could live with a boat up to say 150 lbs. Above that, you will need to install one or two inspection ports to dry it out. It is not going to dry out thru that little drain hole. BB
I have to agree with Beldar. Set it up on edge and drain what you can, then weight the boat. Two people and a bathroom scale will do it. If it's heavy then your only option is inspection ports.
As an FYI on my new boats before I've even sailed them I add inspection ports. One in front of the center board trunk and the second under the bridle. I put the bridle one in as where the boat sits on the beach is sloped so any water that does get in I can sponge out at the rear post. I also add a Fat Bag to the front port. Make a good dry stroage for extra wind indicator string and cassette tape, and my stainless handyman tool.