Yeah - I realise the wrong tool was used and kinda bummed by it should've done my research before doing what I thought would work.

With regards to the pipe cutter, yest it's a type that has the circular roller and two other roller/guides on the other end. I didn't cut all the way through, I used a saw for the final cuts to get all the way through, which I think could have caused the fraying on the inside. I used a little super glue along where I made cuts and also a little inside the steerer tube, but will use a fine grit sandpaper tomorrow to smooth out the insides.

The bike store guys told me the fork is fine and as there are no visible cracks on the surface it should be fairly stable but I'm just so paranoid of a catastrophic failure. I use the bike for commuting and can't afford to have it snap/crash on me.

Also the plug I got was the one the guy gave to me and he said it would work, was he right? I can't seem to find any compression plugs online for a 1" carbon steerer... they seem quite rare.