MacBook Pro bottom of screen cracked

If Apple won't cover it under warranty, then you can cut a piece of black electrical tape to put over the broken section to help prevent the break from getting worse. The damage is already done if Apple won't repair it under warranty although if you have AppleCare+ you can get a reduced cost for the repair ($99 US).

Just an FYI, I have replaced just the Bezel before, but it is very tricky to remove without causing more damage to the Display which would then definitely require the whole Display Assembly to be replaced since very delicate & fragile cables are located directly beneath the whole length of the Bezel (it is the orange you see in the picture). Unfortunately this is not something Apple will do nor is it likely any Authorized service provider will do so. It is not something a regular user or even most techs should try because even I will sometimes make a mistake when removing the Bezel and I have lots of practice & experience.

I would suggest taking it in to see an Apple Genius sooner than later. They may cover it via Warranty and or AppleCare, but they also may say it was caused by the user and a piece of grit, dirt, crumb, etc. but the sooner you get it looked at the better.

Here is the support link for Apple

Genius Bar Reservation and Apple Support Options - Apple