Q: Can I use my iTunes money to pay for the 9.99/per month instead of how it is setup? And if I can, how?

Hello Ally, 

I understand that you would like to use your iTunes credit to pay for Apple Music $9.99 membership cost. Let's see how you can do that.

You can use your iTunes credit to pay for anything through the iTunes Store as that is hit first before your card on file. You will need to have a credit or debit card on file to cover any expense that is not covered by your credit. If you don't have one on file, then it will not bill to the credit even if you have enough to cover the entire expense. The article below explains how items are billed through the iTunes Store.

How iTunes Store purchases are billed
https://support.apple.com/en-us/HT201359

Take care