Great question! 

This verse does not teach that there are other gods, nor does it teach that everyone is a god.

In order to understand this verse we will have to look at the context of John 10 and of Psalm 82 (since the quote "I said, you are gods" is taken from Psalm 82)

In this section of John 10, Jesus has claimed to be deity.  In reaction to what He said, the Jews picked up stones to stone Him for blasphemy (John 10:33). 

Jesus quotes from Psalm 82:6 "I said,  You are gods".  In this Psalm the "gods" being referred to are human judges or rulers who have not judged fairly.  God brings a charge against them for this and says even though they are "gods" they will still "die like men"- vs 7.  In other words, the term "gods" is used figuratively, not literatlly since they will die. These human judges and rulers were to act as representatives of God Himself and judge/act fairly but they didn't. 

The Scripture teaches that there is only one God
God says in  Isaiah 44:8 "... is there any God besides Me, or is there any other Rock? I know of none."