Nothing to worry about, it looks like a natural mutation that happens from time to time.
this site enplanes some of them may see in your growing years.
https://www.growweedeasy.com/7-common-cannabis-plant-mutations
Happy Growing!
If it hasn't repeated on other leaves u should be ok.
My guess if it gets worse is too much water...
But I really don't think it's anything to worry about