Hello Madeleine, definitly make sure you are using a greyscale canvas that is 513 x 513, just as Hooli previously stated, but also make sure your heightmap follows these guidelines:
- Consisting of only one layer,
- Saved in a .png file format,
- Saved as "mapnameTerrain" (This method seems to have worked for some, however not naming it that is probably fine too.)
- And alpha channel is turned off.
If none of those work, try changing your game's rendering system.