It could be a minor nute burn from over fertilized soil. Depending on what you used as a soil a lot of soils are pre ferted and can cause problems for a young canibus seedling. I would def invest in a PH tester so you can dial in the exact problem. The pics also show drooping of the leaves, possibly from over watering. If they are firm and drooping it's over watering if there dry, brittle and drooping it's under watering. To me they look plump and over watered and possibly over nuted from the soil. An easy fix with a PH meter and time. Congrats on the mutant btw lol