From the picture it looks like you have to much material wrapped around the frame. Do you have burlap under the Naugahyde also??? the burlap and cotton pad should be hog ringed to the seat portion of the frame.
All you should have wrapped around the lower flange of the frame is a single layer of upholstery fabric. The barrel clips are tempered spring steel, I'm surprised you could spread them any with out breaking them, usually if you push them beyond the yeild point they will snap in half rather than bend.
DG
I only have the fabric wrapped around the frame. The burlap is hog ringed to the seat with the cotton on top of that.
Heck, when I tried to put the clips onto the frame without the fabric there it was still fairly hard. I had to tap it on with a hammer.