You're signatures were probably not all one length, which is fine. I find uneven pages can give the journal more of an authentic look. But if they are sticking pretty far out from behind your covers, trim them down with an exacto-knife or scissors.
Viola! You have upcycled an item that won't have to go thru the recycling process (which is not always as green as we'd like it to be) but won't have to be, as well as created yourself a new journal or lyrics notebook practically for free!