Is it possible to reset my vote on that answer so I can properly upvote it?
It would be if the post got edited, moment in which you would be able to re-cast your vote on the answer.
However, editing just for you to be able to change your vote doesn't seem a proper course of action to me... unless the post could use some edits in first place.
I suggest that you just let it be; it's 1 rep after all (and 2 for the answerer), so nothing that an approved edit or upvote received can't solve. I too have sometimes miss-clicked a post, but when I do I try to immediately change it (as you have a period in which you can freely do so).
Next time try perhaps double checking the vote action you casted, to avoid further incidents.