Isometric Tilemap Problems

I am trying to draw isometric tilemap tiles in GIMP. However, I don’t know how many pixels the default diamond is, and I tried working under many different configurations. I also tried working with one of the assets, which didn’t work like it did in the demo video. Instead of snapping in nicely, the tile was way too big, images included below. Can someone give me a fix? Thanks!

159028-screen-shot-2020-05-09-at-110620-pm.png

did you solve your problem? i have the same issue and i don´t know how to fixed. Thanks so much

height is 50% of width