Error in initial claim

Kaddy

Hello, I wonder if some one can answer my question?
I claim universal credit and pip, a complete error on my part when filling out initial u.c forms, (while in a flare up of my illness) I failed to add my private pension contributions per month! While talking to a colleague she said I’m missing part of my allowance due to this. I have put a message on my journal explaining, my question is would this be backdated albeit an error on my part? This has been since 2018! Anyone have any idea? Thanks