You received your Morta fixed knife with its leather case but you cannot insert it fully into the sheath, which seems too narrow?
This is because it’s new and the leather of the case needs be stretched to fit your knife.
Here’s a short video to show you how to proceed :
When you slide the knife into the case, you will see that there may be some disproportion between the case and the knife, whereas in fact there is none at all.
Both the knife and the case are new; you need to swivel the knife to force the blade and handle into the sheath. In this way your knife will be fully protected, even though this step is a bit complicated at first because the sheath is new.
After two or three uses, the sheath will rapidly adapt to your knife for a perfect fit.