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A temporary temperature spike is not a good thing but is not necessarily fatal. It happens more often than we would like. What you are seeing is air temperature. The egg itself is a lot more dense and it takes a lot longer for the core temperature of the egg to actually change. So I'd just keep on as if nothing happened. Often you will be fine.
Many people get it wrong when they count the days. It's logical that day 1 should be the day you put them in the incubator, but that is wrong. An egg does not have 24 hours worth of develpoment 2 seconds or 2 hours after it is put in the incubator. It takes 24 hours for it to have a day's worth of development. One way to remember it is that the day of the week you set them is the day of the week they should hatch. Since you set them on a Monday, they should hatch on a Monday. And lockdown should be after 18 days of development. So, since you set them on March 26, lockdown should be about the same time of day on Friday April 13.
This hatch after 21 days of development is theoretical. It often does not happen that way. Many different things like heredity, humidity, how you stored them before you incubated them, how old they were, and relative size can make a difference, but the big difference maker is the average incubating temperature. If you incubator is running a little warm, the eggs can actually be pipping when you go into lockdown. That happened to me before I adjusted the incubating temperature. I still had 70% hatch. If your incubator is running a bit cool, they can be that much late. Especially with your first hatch with the incubator, you don't know what will happen. It can be nerve-wracking.
The main thing with lockdown is that you need to go into lockdown and raise the humidity before they pip. For the first time with your incubator, that can be a little uncertain. So until you get some history with your incubator, I suggest you try to get lockdown pretty close to the theoretical time. You can adjust that if you wish after you get some experience with your incubator.
Correct humidity during incubation is something that is different for each of us. We have different incubators and different conditions. What works for me might not work for someone else. My first time, I followed the instructions that came with the incubator and even with the temperature problems, had a 70% hatch. The humidity inside the incubator can vary quite a bit with the same reservoir filled depending on ambient humidity. My humidity varied from the mid-30's to mid-40's with the same reservoir filled during my last incubation. What I suggest is to try something and be fairly consistent throughout incubation. Then analyze your hatch to see if you need to change something. That's why your instructions probably said to do a test hatch with inexpensive eggs the first time to work out the bugs.