Relax. Take a deep breath. I know, easier said than done. I still get concerned when something unusual happens.
That 21-day thing is just a guideline. It's not unusual for eggs to be a couple of days early or late, whether in an incubator or under a broody hen. There are different reasons for that. Average incubating temperature is a big one but there are other possible reasons. One of the hardest things to do right now is to be patient but patience is your best friend. There is nothing you can do at this point to help but you can cause harm.
That kind of humidity swing is not an issue, it will not cause a problem. You don't want a temperature spike to dangerous levels but a temperature drop is not a huge problem as long as it's not really cold for extended periods. At that stage the chicks are generating a lot of heat of their own inside the egg. Even earlier in the incubation phase they can manage some periods of cooler temperatures.
I know it's nerve-wracking, especially your first time, but I haven't seen anything in your posts that I'd be concerned about.
Good luck!