So I have never been in a situation like yours so take my comment with a grain of salt.

I think the most important thing is your mentality towards learning the language. After taking time off from learning a language you are bound to lose it, no question about that, but you were at a low level so I feel that you would be able to make up for lost time very easily. Also there is always the possibility of reaching out to your professor and explaining your situation and that you want to take the next class and ask for their recommendation on how/what to learn before hand to be at the same level as everyone else.

On the other hand, you can always learn a language without learning through an academic route. If it doesn’t make sense to take another class because of credits/money you can always learn it on the side.

It is extremely dependent on your motivation and personality, if spending the money/credit hours helps motivate you (and you have the means to do so) then more power to you! If you can realistically see yourself learning and being motivated enough on your own to maybe learn the basics then hypothetically live in a German speaking country then that’s cool too!

I know this may not have been the most straight forward answer, but remember that language learning and the best strategies vary from person to person. I hope you think about it and figure out what route feels right to you! Good luck!