First grow. Nute burn?!

Yes, some nute burn and a calcium deficiency too. Nothing you do will fix these issues this late in the plants life, you only have between 7-14 days before harvest.........these issues affecting your plant right now started 3-5 weeks ago already. Dumping gallons of water is not great either, it can release even more nutrient salts from the substrate, which is the root cause of the burning in the first place. Flushing before harvest involves stopping all nutrients and additives for 10-14 days before the expected harvest day, giving just plain water in normal amounts and at normal intervals and then the plant will "flush" itself naturally. Drowning your plants does not achieve anything, unlesss you have given an extreme overdose of fertilizer and immediately want to rinse it out of the substrate. Over fertilizing to the point of the plant being burned then applying lots of water will not cure the damage that has already been done. Also, never, ever grow at 24/0, all cannabis plants NEED "sleep" to function metabolically correctly and to have a normal and completed daily photosynthesis cycle. 18/6 is optimal for plant growth.............cheaper too and less taxing on your equipment also. A plant with an incorrectly functioning metabolism will always have more and bigger issues in general. Maybe try photoperiod fems next grow, autos are not the best choice for beginners, you will learn a ton more growing photo fems and they are far more forgiving too of small errors.

looks more like calcium issues, and a lack of. maybe a bit of burn on the tips but nothing crazy. After your flush did you give them a standard dose of feeding? Or are you flushing because you want to harvest??? Flushing is a great tool to correct issues in the medium that could turn catastrophic. but to do it arbitrarily for harvest is bro science and not needed. just water last few weeks, dumping copious amounts into the medium is just stress and wasteful.