I think /unvote would include your vote as a skip, so if you skipped you could probably do /unvote and it would take it away.
Also, I just thought of this, what if you want to change your vote?
Let's say Breeze is winning with 9 votes, and that's not the map you want to play, and you voted for Fallen Empire which has 2 votes from you. But then there is also Holiday Resort, which you would much rather play, with 8 votes, so you can unvote your Fallen Empire vote and change it to Holiday Resort so that it has a higher chance of winning.
There are many ways to use this command, not only to fix mistakes.