I've done the same thing twice over the years (that I recall). Both were solo trips. The first time I launched my old 16 ft flat bottom off a gravel beach then parked the trunk. When I came back I realized my mistake. I put the plug in and bailed as much as I could then launched and tried to get up on plane for the water to run out. That was a huge mistake! I almost swamped it and that old boat didn't have flotation. I was lucky.

The second time I launched at Portage Marina on Lake Michigan, again a solo trip in my Tracker Magna 17. I backed the boat in and while I was making ready the launch attendant casually asked if i remembered my plug. I thought about it for a minute and couldn't remember. So I secured the strap and tried to pull the boat up the ramp. No way! It was about half full and I couldn't get enough traction on the wet ramp to move it. So I turned on the bilge and waited. And waited. And waited. It must have taken 20 minutes for the bilge pump to get all the water out. At least that boat had flotation, but I'm glad I didn't launch and discover my mistake halfway down the ditch.

Be safe. Take the extra time to make sure everything is right before launching, including testing the bilge pump.
Bordy