Hey mate, yes that's wayyy too close. Your going to fry them. I'm a little ahead of you and wont be giving my girls that kind of ppfd. I'd recommend moving the light to 18 inches, if not a little higher when it's on 100%.
Giving too much light will just stress them and make them grow slowly. You want to gradually increase the amount of light and pay attention to what your plants leaves are doing.
Go check on them an hour before lights out, if the leaves are still pointing up then you're not giving too much light. But if they have dropped then it's a little too much. The earlier the leaves drop will tell you how much over you are giving.
Hope this helps 🙂