Really feels like an image resolution issue. If I remember (though I could be wrong here) Renpy does not auto scale images, even backgrounds. You have to either resize the image to the screen you set Renpy to use or use the Image Manipulators methods to sale it appropriately.
You may be able to also use something like Zoom to deal with it but most info I am finding is resize the image to the resolution you are using for the game. Here are a few links you may find helpful though and best of luck to you!
https://www.renpy.org/doc/html/displayables.html
https://lemmasoft.renai.us/forums/viewtopic.php?t=18421