To clarify is this the similarity score rating? I've not had a lot of experience with it but 23% does seem a little bit high compared to some of my scores. It depends on the type of work though, like for code you'll naturally get a higher score than you would for an essay of similar length because it's a lot more structured.
We've been told that they look at the distribution and check if it's bimodal, basically for any given task there will be a certain 'expected' similarity, and then anything significantly above that might get flagged. For this task it might be 10% or 20%, or whatever, but as long as you fall in the main bulk of student similarity scores, it should be fine.
I would recommend looking at what it's flagged as 'plagiarism' 'cause I've seen similarity scores of 10/15% just from phrases like "at the Large Hadron Collider" or "electrons and protons". Also citations often flag up, so check if that's causing issues.