Sometimes, if you have a feeling a class is just not likely to pan out, you can go with your backup. And that way, you are also moving toward something. And you're not saying the other class is wrong for all time, you're just saying not for you, not this semester.
'May I sit in a couple of classes the beginning of this semester?' You can ask the professor (and keep it short, keep it simply). Or, you can just show up the first couple of classes before the add deadline. I think either way is perfectly fine. And either way, you have scouted out this backup class, you have seen what they've covered, and you can seamlessly make the move.
Check when is the last day you can add a class. This might be a good card for you to play.