While it's technically true you can only book FPs for the number of days you have ticket entitlements, I have had the system glitch and allow me to book extra days. For a trip last year a member of our party had a no-expire ticket and we were sure it only had 1-day left but the system let me book FPs for 7 days for this person. I called Disney to verify the number of days and every one said there must be more days since it let me book FPs. Fast forward to our trip and after the first day of the trip he received an email saying his FPs for the rest of the trip would be cancelled if he did not link a ticket to
MDE within 24hrs. We were prepared for this so he purchased a ticket and all was good.
Hopefully you do have more days then you think left on the ticket but wanted you to be aware that sometimes it's just a glitch.