I would just leave it in for now and not worry about it. You can try to remove it again after you've run the boat a while, but it wouldn't be a priority for me.
To drain the drive lube, remove the lower plug and remove the top to the gear lube bottle mounted on the engine. When you refill the lube, leave the top off of the bottle again and pump lube in until it fills up the lube bottle.
That's the way I do it normally, I never remove the vent plug. Doing it this way will ensure you have no air in your lube oil system.
2006 Bayliner BR205
A1 Gen 2 1.47
5.0 carb engine