Cardboard flavor typically means it's oxidized (at least with beer it is). So, depending on how you racked, it happened there. I don't believe there's a cure for that (one of the few things that cannot be fixed with time). Other, more veteran mazers might know of a trick, and could post up.
The 'hot' aspect (in your face alcohol) can be aged out. At 8 months old, depending on the strength, it's barely an infant (in mead life). I typically go 12 months before bottling batches at/under 14%. If yours was 18%, and finished dry, I would have gone 18-24 months before bottling. It will age MUCH better in bulk form.