I was interpreting the passage. If as you said above that Christ's sacrifice was adequate, then Paul saying something else about the need for the assembly at Collosus to see him suffer as a witness to the sufferings of Christ. There can be no lacking in the Sacrifice of Jesus, although this verse can be misread to say that and has been.

Do this in memory of me is exactly what Jesus meant along with if you do not eat of the flesh of the Son of Man, you have no life in you.

You are all over the place. Laying down our lives for eachother is about martyrdom, which is an example of suffering, but it is a witness of the sufferings of Christ, not a supplement.

I did not come up with the theory that Collosians is not Pauline, but that does not make it an inspired work from somoene in his circle. We simply don't know.