I thought that Agnostics acknowledged the existence of a God, but they don't know what it is/what it looks like/etc?
No, that could describe deists or maybe people who describe themselves as “spiritual.” Agnosticism is the position that the question of God’s existence is unknowable - which is also the position of weak atheism. If you believe there is a God but think that it is impossible to know anything about God’s nature you are not agnostic because you have taken the position where you believe God exists.