I would call the office that sent you the mail-in ballot. I don’t think you’re required to use it, but it can’t hurt to check. It might even be in the FAQ on their website.
I tried researching it online but got no real answers. If I put in my physical address, the message comes up that I have to use mail-in voting.
Since this is a federal election, I really don’t think they can stop me from voting in person. The only place to vote in town, it seems, is the library.
If nothing else, when I take the DVDs back on Wednesday (or Tuesday) I’ll ask while I’m there. Someone may know.