There are a lot of diff things it could be. Someone mentioned nutrient burn, which is much more pronounced in the presence of heat. Also if dehydrated the plant will be consuming more water, so upping the amount of water (do not choke them though), and decreasing nutrients slightly to let it recover can help. This is a great time to refill your spray bottle, and give them a few minutes of 'rain', ro/di or distilled is probably best for the next 24-48.
Did you say you had just transplanted it? That could cause the necrosis that you're seeing even without the heat/dehydration (which would just make things worse). Unfortunately, unless the soil is bone-dry, or you have packed it too tight, there isn't a lot you can do but baby it and hope. If it's dry down to 2" and haven't drenched it in 2 days water it, if you over watered use a fan to dry it out and poke a few holes with a pencil, If you over packed the soil then very carefully loosen it. You can loosen with a pencil, and by rolling the sides of a flexible pot.
No real way to quickly limit growth, other than hurting it (depriving a plant of light will stop growth, but will also kill it). In flowering it will grow at a slower rate, but will still grow. Plants can grow 1.5-3 times their size in flower.