Best of luck!
I am putting my first hatch into lockdown tonight. So I know exactly how you are all feeling.
Over the last 18 days, here is what I've been able to gather:
A mother hen does not keep everything 100% perfect all the time. You WILL have changes in temps and humidity, some of which look very scary. You just have to roll with it and not stress about it.
These three weeks are going to feel like FOREVER! Yet you'll get to lockdown day and realize you are soooo not prepared for the next step of this process.
(think I might want to purchase a brooder & lights in the next couple of days????)
Eggs that you are sure are doing nothing, will surprise you a few days later.
The thrill of seeing veining for the first time will make your heart pitter patter.
You will obsess and worry and act like a "mother hen" (pun totally intended), but make sure you have fun.
That's all my inexperienced brain can give.....hopefully, I'll have chicks in a few days to prove that I'm giving some good words of wisdom.