Sims 4 Studio - Walls Showing Stretched in Game

I'm re-decorating my sim self's aunt Tina and uncle Jimmy's place. I've made a custom content wall in gimp and when in the sims 4 studio, it displays as i made the wall but in game it shows very stretched out. 

In Sims 4 Studio, this is how it's supposed to look:

In game, it's all stretched out. 

Any ideas where i've gone wrong?

I must note nothing is saved on OneDrive!