First, don't give up hope too quickly. That 21 days to hatch is a very general time limit. When my incubator ran a little warm, I had eggs hatch 12-1/2 days early. If yours is running a little cool, they could be that much late. There are other things that can affect actual hatch date, but average incubating temperature is the main one.
I never trust the thermometer that comes with the incubator. You need to calibrate any thermometer to make sure it is working right. And it needs to be a pretty decent thermometer.
Are you sure you are counting the days right? That is a very common mistake. It takes 24 hours for an egg to have a day's worth of development and, in theory, it takes 21 days of development for the egg to hatch. A good way to remember this is that the day of the week you set them is the day of the week they should hatch. If you set them on a Sunday, they should hatch on a Sunday. As I said, that can vary by a few days but that is the target.
That metal baking sheet was not a problem. Same with the wobbly table. Don't even think about those.
I use a hygrometer to tell me when to add water. I don't worry a lot about what the humidity actually is. Some people make a science out of it and weigh the eggs to determine how much moisture is lost to make sure the humidity is right, and they probably get better hatches than mine. But mine are usually pretty good. I did it the way the instructions that came with the incubator said and that worked for me, so that's what I do.
I've also had really bad hatches. The one I have now due this Tuesday is a bad one. 17 of the 30 chicken eggs never developed at all. Hopefully most of the rest will hatch. These were eggs I got from someone else, but they were not mailed. I picked them up locally. All five turkey eggs developed, so I'm not convinced the problem was my incubation technique. Not everything in an incubation is under your control. Sometimes things just happen.
But I suggest you give it a few more days. Don't lose hope too quickly. And good luck!!