I got a notification that I had a -1 reputation change, and when I checked what caused it, I found that it shows I down-voted this answer. I didn't vote on it though; I must have accidentally hit the button while scrolling on my phone, and now it won't let me change it (it says the vote is locked). Can this be corrected so the user doesn't get an undeserved down-vote?
Yes, an accidental vote can be changed if the post has been edited since you last voted. Refer to the following Stack Exchange FAQ:
Search for the "Limits on changing votes" section:
you may remove your vote after every time the post is edited (excluding grace period edits).