lily-book extending margins

[Alberto Simões]

Hello

I am using lily-book for some time (more than 282 musics so far), but 
for this one, I added instrument names, and with this extra space that 
they take, the score gets out of the margin at the right.

You can see the result here:

  http://eremita.di.uminho.pt/~ambs/sctb.pdf

Any hints?

Thank you
Alberto