Your sprite is too small I think. RPG Maker MV has bigger resolutions than ace or previous versions, that's why ur sprites will look weird or won't be accepted.
My Recommendation:
1. Open the character generation tool inside your project editor (the small actor sprite icon)
2. Export the damaged sprite to a location where you can find and edit it.
3. Open the exported damaged sprite in an image editor program (gimp, photoshop)
4. Insert your sprite as a new layer and scale it to the right size. Take the exported file as a template
5. Delete the template so that only your sprite is left
6. Export the image to [Game Folder] / img / characters
Hope I could help you mate!