Did you provide a credit card for any downpayment?
At this point I wouldn't worry about on board credits or price protection. You may want to be more concerned that your cruise travel plans go smoothly.
From the information you provided, I would be concerned.
If you didn't pay anything down via a credit card......just call an NCL TS and they can provide booking, pricing, on board credits.
If you need premium assistance from an NCL Travel Specialist....we can provide a direct link for you. Just send us a PM and we can provide you with our #1 contact from NCL.