I wouldn't use JB Weld on this plastic (its not your typical model kit type of Styrene plastic, it's more like the softer PVC Piping plastic as evident from your cutting and all the burrs it creates making it difficult to keep a smooth line)... it could warp it while the JB Weld is curing and cause it to melt. When JB Weld cures, it generates heat. Its great for metal items, but not for plastics. I had a similar problem with Squadron Green Putty awhile back that the entire surface I had used it on melted because the putty got too hot for the softer plastic (like this is made out of). I would recommend using either Magic Sculpt or Apoxie Sculpt. It doesn't heat when its curing and you won't have to worry about doing more harm then good.