What is the difference between pan-en-theism and omnipresence?

The way I understand this idea is that pantheism says that God is in everything. Hence, pan meaning a wide range of area, and theism which relates to God. God is much bigger than pantheism because The Bible says he has to humble himself to be able to fit in the universe he has created. We cannot comprehend the bigness of God with our finite minds. Colossians 1:17-18 tells us that God holds his creation together. Imagine what would happen if God stepped back and abandoned his creation for any amount of time. By believing in pantheism, you are limiting God's bigness even though you probably won't agree.