Hi Yiuriel,
There is some ‘tessellation’ that automatically happens with landscapes. If you change your viewmode from ‘Unlit’ to ‘Wireframe’ you’ll be able to see it in action. (It sounds like this might be what you’re seeing)
Otherwise I’d experiment with the ‘resolution’ of the landscape when creating it, and/or fiddle with the LOD settings in the landscape details panel.
Hope that helps! Welcome to the forums!