All of my prints are stretched!?

So everything I print is stretched. If I print a coin, it comes out oval. If I print a square, it comes out rectangular. This was supposed to be a human skull, but came out more like an alien! I did a few prints over the weekend and all of them are stretched like this.

What could be causing this? It looks fine in Chitubox Pro, the aspect ratios are fixed at 100% width and height, looks fine when it's sliced etc.

Is this something going wrong at the software end or something to do with the settings I am printing at? Should I try a different slicer or a different resin perhaps?

- Mars 5 Ultra using default settings
- ELEGOO 8K Standard Photopolymer Resin 405nm in grey
- Model is about 1 inch in width

https://preview.redd.it/kgj6quz4tbee1.jpg?width=900&format=pjpg&auto=webp&s=0f054cc22d681fcbaf43207557e0d890638de242