Problem with heightmap import

I try import heightmap and get this
How to stretch heightmap all over the landscape grid?

you cant just hit fill world when you import an height map, that will just pad the file to fill it, you need A: a higher res map, or B: import it without hitting fill world and use the scale tools to make it the size you want, however that’s not the best idea as it will have a very low density per UU