It's impossible to miss the topic of God wanting you on his side if you've even bothered to read a small section of the bible, so I'm not going to waste time going into that. According to other usages of "marks" in the bible, they are given in reference to someone's thoughts or actions; aka forehead or hand. The prophecies in the bible are always fulfilled, but not always the way we think they will be. Usually they have a spiritual aspect to their fulfillment, and I believe that the marks on the hand and forehead are not so much physical markings, but us showing our allegiance to the Antichist in our thoughts and actions.
I have not personally dug into what the 666 means, but I do know that is pointing toward a specific man. A man who will be similar to the man spoken of in Daniel, who was later fulfilled in Antiochus Epiphanes which was detailed during the time of the Maccabees. That is what this man who is represented by 666 will be like, and he will also be similar to who Christ was during his first coming in many ways. He'll do miraculous things in our eyes, which very well could be scientific wonders, but in the end, he'll bring peace to Israel and then will show his true colors.
It's one thing to worry about things, but if we look at what the intent of Revelation is, it is to bring us hope. God wins.