If you take off too much, you can always trim back the tinned together shielding. If you don't take off enough and you tin the shielding, you will be SOL for pulling more of the shielding apart, and you will have to start over.
I made it too short on the first end I did and had to do it over, and since then take about an inch off and trim them so they fit, just to be safe. Just make sure to trim them back, so you get the insulation as support, as JohnR said.