Hi Daisy,
What a nice idea for a project. I’m afraid though, that resin isn’t what I would use to preserve a stuffed animal.
If you can imagine what the stuffed animal would look like when it gets wet, that’s what it is going to look in resin. There will also be a lot of trapped air inside the stuffed animal, which will release into the resin. It’s going to be hard to have your resin be bubble free.
I wish I had better news for you.