Landmass layer painting issues

Hello! I’ve been following along to the “Building natural environments” tutorial on the Unreal Engine YouTube channel, however, I have ran into a problem; whenever I apply a layer from my landscape material (Rock), it is half blended with my grass texture, as seen here. Does anyone know what might be causing this? Here is an image of my terrain material.

I am a beginner with Unreal Engine, so please forgive me if this is a really easy problem to fix!