Re: feeling like you pray more from your forehead - Well, that’s pretty normal. Of course, a lot of people picture themselves praying from all kinds of places. It’s not good or bad; it’s just a quirk.
Re: the main meaning of the people being sealed on their foreheads - When early Christian people were Baptized, they were given chrism with a small Sign of the Cross on the forehead. This went along with the vision of Ezekiel about angels marking God’s faithful people with a cross/letter Tav on their forehead, just like shepherds would paint a sheep marking of a Tav on the sheepfarmer’s sheep.
So that carried over into Revelation, and many of the early Christians made a small Sign of the Cross on their foreheads, to bless themselves before they did any kind of activity.
Later, people began to make the big Sign of the Cross over their whole bodies; but the tiny Sign of the Cross is a little older. And that’s still how priests do certain Baptismal blessings and how they give us ashes on Ash Wednesday.
So yes, if you have been Baptized as a Catholic, you were sealed with the Holy Spirit, and some of the physical signs of it were the water, the chrism, and the cross on your forehead. (Along with crosses on other parts of your body, like your hands.) You are marked and sealed as one of God’s flock, and as a consecrated Temple of the Lord.
Obviously, one of the easier meanings about the marks of the Beast are that they are the opposite or fake version of Baptism, because there’s an entirely different mark on the forehead (and hands).
Anyway, here’s Ezekiel 9:3-6 -
"And [the Lord of Israel] called to the man [an angel looking like a man] that was clothed with linen, and had a writer’ s inkhorn at his loins. And the Lord said to him: “Go through the midst of the city, through the midst of Jerusalem: and mark Tav upon the foreheads of the men that sigh and mourn, for all the abominations that are committed in the midst [of Jerusalem].”
And to the other [angels], He said in my hearing: “Go ye after him through the city, and strike: let not your eyes spare, nor be ye moved with pity. Utterly destroy old and young, maidens, children and women: but upon whomsoever you shall see Tav, kill him not…”
So you see that Ezekiel was having a vision of a sort of New Passover, where the recording angel was inking a sheepmark cross on the heads of those who were faithful. That mark would save them from the angels of death, just like the lamb’s bloodmark painted on the Israelites’ doors saved their firstborns from the fate of the idolatrous Egyptians’ firstborns.
Re: centering prayer - It has some serious problems, and I agree you don’t want that.
The good news is that there are many forms of contemplative prayer and meditation which are totally A-OK, and much more interesting than “centering prayer,” too. The Jesus Prayer is one of the “quieter” forms of listening to God. There are also forms of prayer that use more overt thought, like lectio divina, meditating on the Mysteries of the Rosary, Jesuit use of the imagination and the senses for understanding the Bible, and on and on and on. No matter what form of prayer you use, all prayer tends to become more contemplative as time goes by. (If you keep at it, anyway!)
The late Fr. Dubay’s books and TV shows/EWTN podcasts are quite good introductions to this world of prayer. So is St. Teresa, or even St. Therese. But there are tons and tons and tons of contemplative Catholic saints who were good teachers of prayer.