No, you can apply the fusible interfacing before cutting out your strips. The difference being that you may waste some of the fusible interfacing doing it this way but it’s not that big of a deal, especially since you’re doing strips. Also, the interfacing piece tends to be cut smaller than the fabric piece because you don’t need interfacing in the seam allowance. If your interfacing is light enough and not causing extra bulk under your quilt seams, then I wouldn’t worry about it. good luck on your quilt! 🙂