Sprite repeats itself when using shader

I am using a custom shader for a custom material to highlight sprites but when applying a default to my MainTex my sprite seems to repeat itself and I have no idea why. Anyone a clue? I don’t even know where the grey part in the top right corner is coming from because that’s not even in te original sprite.
Setting the texture of my sprite to Clamp instead of repeat didn’t solve the issue.

Every time I highlight an sprite it comes out weird now

Thanks in advance!