Hi Susan,
The short answer is 'no'.
The detailed answer is as follows:
Here's some of what Revelation says about the mark.
Rev 13:16-17
16 "And he causeth all, both small and great, rich and poor, free and bond, to receive a mark in their right hand, or in their foreheads:"
17 "And that no man might buy or sell, save he that had the mark, or the name of the beast, or the number of his name."
You can't buy or sell without taking the mark - obviously everyone buys and sells in various means at the moment, and that thumbprint has no bearing on your purchasing ability.
I believe that the choice to receive the mark will be as such that you will *know* (as a Christian) that you would be choosing eternal damnation should you choose to accept it.
Many people think that the mark will be a bar-code, or an implanted microchip. This is because these seem like realistic ways that you would be able to buy & sell.
I would reccomend reading through revelation - it took me a while to try to face reading it because I thought it would be so full of symbolism that I wouldn't be able to understand any of it. While there is a lot of symbolism in it, it wasn't nearly as bad as I thought, and I actually enjoyed reading it!
I hope that relieves your fears - you definitely have NOT taken the mark of the beast.
God bless,
Tris