OK .... let me recap what I think you said ....
You purchased enough flannel fabric to do the entire thing then bought more soft fuzzy stuff for the back that you liked better .. right? So now you have more fabric than you needed. I would read the pattern and then look at the pieces - cut out what I needed for the top from the flannel then cut out the pieces from the fuzzy stuff for the back.
I googled the pattern to see what you were trying to make. It appears that in the image I saw that the edges/seams were left raw like in a rag quilt. Just one question - I am thinking that this warm fuzzy stuff might be "minky". If so, you may have problems with the raw edges. Minky (if it is) has a tendency to shed its fuzz at the cut edge. I have worked on it but never left the edge raw. Just check the edges - in case the shedding is too much.