Peg, you may not listen to this but it's an attempt to help a bit.
You have been lied to! The sources you have used for your information are not honest. They leave facts out, make facts up and do whatever else is possible to mislead you.
You can't and shouldn't accept that as correct right away but you must start to entertain the possibility if you are going to learn anything. The dating question is just one area where they lie and lie again.
Get yourself a baking dish and fill it with water. Next, take a coffee cup and fill it with something so that it will not float in the water of the dish. Seal it off and then place it in the dish. Make sure that the cup is tall enough so that some of it juts above the level of the water.
You now have a model of the earth. The part of the cup jutting above the water line is "dry land."
I think this model is incorrect. At least part of the "land" is deformable. Mountains rise and fall over time. If your cup can be deformed then it can be flatten out and under the water.
As noted your calculations for Everest must be out of wack.