Can personality actually change, or am I stuck with what the test says?

It changes. This is one of the clearer findings in the area and it reverses what the field believed for decades.

The long-run picture: traits shift systematically across adulthood. On average people become more conscientious and more agreeable and less emotionally reactive from their twenties into middle age, without trying. That is a population average with plenty of individual variation, but the direction is well replicated. Traits are stable relative to other people, which is what "stable" meant in the older literature — it never meant fixed in absolute terms.

On deliberate change, the evidence is more recent and more encouraging than most people expect. Reviews of intervention studies find measurable trait movement, appearing within weeks and persisting at follow-up, with the largest effects on emotional reactivity. Two qualifications worth having: the changes are real but modest, and they come from repeatedly doing the behaviour, not from insight about it. Understanding why you avoid conflict does not change how you handle the next one.

So a low score is a starting point. The practical part is that the broad trait is the wrong unit to work on — it is an average over facets that move independently. "Low conscientiousness" might be poor initiation with fine organisation, or the reverse, and those need different work. Same for agreeableness: trouble asserting a position and trouble reading a room are different problems that land in the same score.

Which argues for the same thing either way: find which facet is actually low, work on that specific behaviour, and retake in a few months. A retest that shows movement on one facet while the others hold is much better evidence than either the original score or your impression of whether it worked.