The water we sail in is not pure H2O. It carries many passangers-sand, dirt-that it will leave behind when it changes its state from fluid to gas inside your board.
Sounds like your board will be ok. You just have to make sure you open the vent every time you are done sailing or if you leave your board in the sun for an extended period. There are a couple of tricks to prevent you from repeating the error.
1. Use a marker to mark a line where the vent plug is tight. When you loosen the plug you will see it doesn't line up with your mark.
2. If you use a two-bolt Chinook system put your vent plug inside the base upside down and close the base. The plug won't get lost and you can't put your extension into the base with the plug in it.
3. Put your fins screws in a plastic bag with your vent plug. Every time you go to attach your fin you will see the vent plug and remember to put it in.