This will Rot.

You left grass under it which will let weeds grow between your planks. The sleepers are in the dirt with no drainage, These will rot in no time. You will have problems with this in 3 years or less depending on the amount of rain you get. All dirt should have been removed and it should be set on gravel to have any chance at all of lasting. But it looks nice (for now).

Ed.The sleepers are H4. Designed as 'in-ground' treated wood so they shouldn't rot too quickly. . It's also on more of a slope than it looks. But you are right, a gravel base would have given it more longevity. Good tip.