Story endings can be hard. Not only because you have to say goodbye to your characters, but it feels like this is the moment that will make or break your story.
A successful ending can be hard.
But here is one question you can ask yourself to help find the right ending for your story: Did you solve your story?
Whatever problem was moving your story along, was it resolved?
Did your protagonist grow up? Did they attain their goal? Was the world saved? Did the couple get together in the end?
There are a lot of things to consider in order to create a good ending. One of them is to make sure that you have satisfied the promise you made to your reader in the first pages of your story and showed your characters either succeed or fail in the goal that was moving everything along.
Start there and see where your ending goes based on that.