What! You got a plug with yours?
My boat didn’t come with a plug. Instead, it came with a stage prop that was supposed to be a plug, but was not capable of plugging the hole.
OK. I exaggerate. It would have been capable of plugging the hole if I had applied a large dollop of silicone sealer along with it.
At the factory the hole in the fibreglass was drilled at a 20 degree angle to vertical (that, or the drill wandered) so the “plug”, yeah, let’s call it that, because of its poor construction, was not able to be sufficiently tightened to seal the hole. Instead, the “tin foil” deformed. Assuming you could insert it into the hole with it released (loosened on the threads) in the first place.
Check the hole too, it might benefit from some dressing or smoothing with a file.
After some shopping (there are lots of “junk” plugs in stores) I found one that had a pliable soft rubber body that would expand to give a good seal. I attached a lanyard to the old one and wrapped it around the bowl as a spare, better than nothing if the other is lost or broken.
So, I feel your pain.
In all seriousness the role of the plug is not really as critical as you might think- if it leaks the bowl will prevent, in most cases, the boat from swamping. But water sloshing around inside the boat and bilges is certainly a nuisance.