How do I preserve my mushroom stuffing for freezing?

But, as Catija indicates below its not clear whether you are stuffing mushrooms or whether the stuffing contains mushroom. Based on the other stuff used I am going to go ahead and guess that you are stuffing mushrooms with this, but I am going to make this and if/then answer to cover both cases.

If the stuffing contains mushrooms:

you have to decide whether it's ok for the mushroom to get mushy, then you don't have to do anything special, just make sure it's in a freezer bag and get all the air out. However, If you want your mushroom to stay firm, then don't freeze it, and wait until you get closer to the day you need to use it, then you can refrigerate it for a day or two.

If not:

I think you'll be just fine to freeze it. I might freeze the portions on a cookie sheet first before putting into a bag, it will make thawing swifter and more painless.

Here you still need to consider what kind of freezing you are using. Dry freezing dramatically dehydrates food and shortens the shelf life. I found this out at https://beezzly.com/can-you-freeze/can-you-freeze-gravy when I decided to freeze the mushroom gravy. Homemade mushroom gravy, once cooked and stored neatly and properly, will remain usable for up to three days in the refrigerator.