sharkdriver, your first post. Welcome to the forum. How about posting a photo of your setup?
In days of old, people thought the UQ had to be cinched tight at the ends. That looked pretty when you weren't in the hammock. But you know you get the best lie when you are a bit diagonal to the center line. That means your feet and shoulders are pushing out at the sides. If the ends of the UQ are cinched tight, that "push" will create a gap for heat-robbing air flow. Nowadays, ends, still gathered with an adjustable shock-cord, are set loose enough so they can "form fit" to the shape of the hammock with a body in it.
Your problem might be here ... these days most UQ's are made with a differential cut. That means the bottom side of the quilt is cut fuller than the top. Without that design feature, if you snug the UQ too tight to the bottom of the hammock, you'll compress the down, the loft, and you'll lose your insulation effect.
Some vendors, like Hammock Gear, have, in addition to a top and bottom, also have a head end and foot end on their UQs. That's because they concentrate more down/loft from your shoulders to your waist. So you attach their UQs with the proper top/bottom and head/foot orientation.
It's recommended by some that the UQ be attached such that full-length shock-cord suspension (on the sides) lift that hammock about 10 inches when no one is in it. That assures the UQ bottom is right up against the hammock body - no gaps. But again, they can do that because of the differential cut. No matter how tight the UQ is against the bottom of the hammock, it will not compress the down insulation, the loft.
So does that give you any ideas about what to look for? It might be that you are not attaching your UQ tight enough, so there are no gaps along the bottom of the hammock. Or you are attaching it too tightly so it's compressing the loft.
Note that a "comfort rating" is just a manufacturer's suggestion. I've found that a 20° rating keeps me comfortable in the low 30s and maybe a degree or two into the high 20s. I would NOT be comfortable at 20°. Each person discovers what works for them.
As that great philosopher, Columbo, would say, "One more thing sir. ..." I'm old. I have to pee at night. When it's time, my body stops producing heat. It's my body's way of ... encouragement. I'm thinking, "I don't have to get up now. I'll wait. Morning is almost here (it's 3 AM)." So I get colder and colder. Then I finally get up, water a tree, and get back in the hammock. Half an hour of suffering when it only took a minute or two to heed the call.
If you're young, don't worry about it. Just one of the many surprises waiting for you down the road