The First Day:
Genesis 1:1 In the beginning God created the heaven and the earth.
1) The verse is only narrating us the summary (story) of the Beginning - God created the heaven and the earth.
Genesis 1:2 And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters.
2) The Scripture is documenting us the actual condition of the Deep before the creation of the heaven and the earth in the beginning.
Genesis 1:3 And God said, Let there be light: and there was light.
3) God brought forth the Light Before the actual creation of the heaven and the earth took place.
The actual making/formation of the 1st heaven took place on the 2nd day Genesis 1:6-8 not on the fist day - Genesis 1:1. The earth was made on the 3rd day - Genesis 1:9-10
I see no "gap" (theory) between Genesis 1:1-2. God does not repair anything good that he makes. He only creates new ones for perfection.
Conclusion:There's nothing wrong with God's Truth as it is written in the Book of Genesis. The problem is the flawed understanding of men.