When I render this flag I made, the contact shadows are extremely blocky. I am very new to Blender and 3d modeling as a whole, so I only know the basics and don't know how to fix this. I'm using an HDR map for the lighting but could'nt find anything useful online... I hope someone on here knows what is going on, because I surely don't :')

I attached an image for visual reference

my flag render with blocky shadows