Why would Jesus tell you not to be repetitious in your prayers when He was repetitious in His prayers?
Are we not to imitate Christ? (1Co 11:1)
Or, are the "vain repetitions" which "the heathen" do (Mat 6:7) a reference to the incantations which the pagan priests use when they pray to their false gods?
If we are not to repeat prayers then, having said the "Lord's Prayer" once, should we never say it again? That would be repetition.
But, you do as you like.
Enjoy
Jesus said his soul was exceeding sorrowful unto death, Mark 14:34. We read in Luke 22:43,44 an angel appeared from heaven strengthening him as he was in agony and prayed more earnestly and his sweat was likened unto great drops of blood falling to the ground.
Jesus was speaking to Peter, James and John in Mark 14:38 as he said, Watch ye and pray, lest ye enter into temptation. The spirit truly is ready, but the flesh is weak. 39 And again he went away, and prayed, and spake the same words.
The Spirit that is Christ was ready to fulfill God's will, but the flesh part of him was weak as he was weakened and in agony as his soul was exceeding sorrowful unto death. Within the flesh part of Jesus he might have been tempted for a moment not to do God's will as this could be why he prayed the same thing three times. Paul taught about the flesh being weak and tempted in Romans 7:23 and Galatians 5:17. Jesus knew before the foundation of the world what He would go through so that would be no surprise to Him, but yet praying the same thing three times He was being strengthen each time until the day was ready.
This is not repetition of vain words, but stages of praying for strengthening of the Spirit for God's purpose. I couldn't even think how this would compare to what Jesus said in Matthew 6:6-8.