The mast is buggered, I will give you $50 for it.
Seriously - it depends on the depth of that damage. If it is one fibre layer that is compromised - bit like peeling just some bark off a tree, then it is fine. A bit of resin would not hurt, but it is not terminal.
But if a crack runs thru to the inside then it
is buggered. Then again, cutting off 3cm of a mast will not hurt it any.
If cutting, tape it up first to stop splintering, sand it nicely afterwards and maybe smear some resin on the end (cut part) afterwards to discourage any splintering