Is this burning on my plant or ? And how to lower ...

That looks like signs of root rot to me. Your keeping your soil to wet, let dry out a bit and water less more frequently . I experience this when cloneing sometimes. To lower temps the best is to get an air conditioner, nothin fancy just big enough for your room. For that yong of a plant I would run 60-65% you’ll see more growth. Lower for flowering around 40-45%. She looks good but will look better if Tom the watering down! If you go on the GH website you can get a feed chart, also has a feed chart on the back of the bottle, follow direct but if I were you I’d at least cut the recommended does by half. As for the gray it’s hard to see might be Mold from your water being to wet! Good luck!