you have multiple issues going on so it will be hard to narrow down exactly which one/ones are causing you grief
Start with the most advantageous - temps. At 45°F, you stress the roots and plant kind of stops growing. Nutrients fail to upload from soil to the plant...this is WINTER!
SO many use heaters to heat up an area, but you have to heat up the tent and do it in a way that does not make hot spots and cause heat stress to plants or parts of plants
Personally, I do LIGHTS on at night, it helps keep the tent warmer when the temps are going down. Get something more between the plant containers and the floor...like a dish mat for absorbing water, they insulate the container (and thus keep roots warmer - cold floors, especially cement, transmit the cold right through to the plants roots). The plant itself can handle colder but the roots cannot.
I went on Amazon and purchased BLACK CERAMIC (can be on at night and not cause light issues)
https://smile.amazon.com/gp/product/B07H4TDZR3/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
I got 150w and 250w bulbs and hang them from the ceiling rods. Turn one on at a time to see what the temps wind up being...do not want to get over 80°F...best is 70-75 and colder when in flower 60-70.
It is easier to stay warm during the day tan night which is why I run lights at night, dark in the day except for the heat lamps
Once you have the temps and RH (it will change because of the heat lamps, then you can work on the substrate - feeding (strength and types of nutes and watering (how often)