The very earliest Christians call him Lord and God
If we want to claim that Christians just made up the stuff about Jesus being God then we need to take into account how quickly they started saying it. It all happens much faster than you would expect something like this to take. It usually takes a minimum of two generations before such a myth can develop and yet we find contemporaries of Jesus saying that he is God.
The earliest Christians were Jewish. When a Jew read their scriptures they were prohibited from using the name of God (YHWH). This was so important to them that we don't even know today what the vowels in this name are because no one ever used them. Instead they would use the name "Lord" when they came to God's name in the Bible. This was deeply ingrained into their way of thinking. Lord = God.
We then find that the earliest Christian creed is in fact "Jesus is Lord". This is not a later development or misunderstanding by the church Christians have always believed that Jesus is Lord.
We also cannot play down what the very first Christians were claiming. All of the first Christians were Jewish and it is drummed into them from a very early age that there is only one God. For someone to claim that they are God is blasphemy and an offence punishable by death. Yet these same first Christians are the ones making the claim that Jesus is God.
Following on from this we know that during a time of persecution Christians were required to take an oath saying that the Emperor was Lord. If "Lord" only meant a ruler or high ranking person then they could have done this easily but instead they refuse - facing execution for doing so. Why? Because saying someone is "Lord" is very significant for them. This is not something they take lightly. Yet we see that this is exactly the phrase that they use for Jesus - Jesus is Lord.