Did the exact same thing a while ago. Initially upside down to pump out any loose water with a wine vacuum pump, then the paper towel wick, then stored right way up for the light water vapour to come out. I estimate I removed a couple of table spoons.
A few years later the board is fine, although I think once you think you might have water in the board, storing with the bung undone is more important than ever. Over time, I guess a little more water vapour comes out every time the board warms up and cools down in storage.
I've now given myself a mental ban on installing the mast base until I have done up the bung screw.