cf. Deuteronomy 6:4; Isaiah 43:10; 44:6, 8 and Genesis 1:26; 3:22; 11:7; 1 Cor. 8:5; I John 5:8
One God
"Hear, O Israel! The Lord is our God, the Lord is one!" (Deuteronomy 6:4)
". . . Before Me [YHWH] there was no God formed, and there will be none after Me" (Isaiah 43:10).
". . . there is no God besides Me" (Isaiah 44:6).
". . . And you are My witnesses. Is there any God besides Me, or is there any other Rock? I know of none" (Isaiah 44:8).
Many gods
"Then God said, 'Let Us make man in Our image, according to Our likeness . . . '"(Genesis 1:26).
"And the LORD God said, "The man has now become like one of us, knowing good and evil . . ." (Genesis 3:22).
"Come, let us go down and confuse their language so they will not understand each other" (Genesis 11:7).
"For even if there are so-called gods, whether in heaven or on earth [as indeed there are many 'gods' and many 'lords']" (1 Corinthians 8:5).
"For there are three that bear witness, the Spirit and the water and the blood; and the three are in agreement" (1 John 5:8).
The Bible tells us that there is only one God in all existence (Isaiah 43:10; 44:6, 8). However, it also mentions "other gods." For example there is Adrammelech and Anammelech (2 Kings 17:31), Asherah (1 Kings 18:19), Baal (Judges 3:7), Chemosh (Num. 21:29), Dagon (1 Sam. 5:2), Molech (Lev. 18:21; 20:2-5), etc.
The Bible is not contradicting itself. When the Bible speaks of other gods, it is speaking of false gods that have no true existence.
Gal. 4:8 says,
"Formerly, when you did not know God, you were slaves to those who by nature are not gods."
See also, Isaiah 37:19 and Jeremiah 2:11.
God tells us that he alone is the true God, and that all of the invented gods of man do not exist except in their own minds. So, we can see that the Bible is not contradicting itself regarding how many gods there are in existence. There is only one.
Note: in the verses in Genesis that have God saying "Let us make . . . , Let us go down . . . , etc.", are clues to the Trinitarian nature of God. God is a Trinity of persons: a Father, the Son, and the Holy Spirit. There are not three Gods--but one. There are those who insist that the Trinity is polytheistic. But it is not. Trinitarians believe in a single being who is God.