If you zoom closely into your traced image you’ll find that rather than being a simple spiral vector it will be either a series of vectors or one single closed shape around the original ‘pencil line’. Fit path to text might have difficulty with this depending on exactly how your trace came out. Ideally you want to import a vector spiral.
I actually created a spiral generator a little while ago to answer a requirement by another LB forum user. I’ll try to find the thread so I can post a link if you’re interested.
EDIT:
Here’s a link to the thread I mentioned.