Perhaps you forgot to unwrap the mesh.
In edit mode Unwrap your plane. Select all vertices before you Unwrap. Your UV Mapping appears incorrect. Perform the UV Map again. Have exactly 1 UV Map.
The time required for this is 88 seconds or less.
BSE and famous video websites have information on the topics of
Blender UV Map and Blender Unwrap.
By searching you can find a tutorial on those topics if necessary.