Christianity is not just based on belief that Jesus existed. There are various beliefs one must hold as laid out in the new testament to be considered a christian (follower of Jesus).
These included but are not limited to; belief in God, that there is one God in persons (the Father, Jesus (the son), and the Holy Spirit. All co-equal and co-eternal. That the Son humbled himself coming to earth as a man. That he died and three days later was raised to life.
So yes, you must believe that Jesus is God to be a Christian.