I teach remedial math at a university, and we use the COMPASS as a placement exam. From everything that I have seen, it does a very good job of placing you. Most of my students are straight out of high school, but I do have several non-traditional students this semester.
I don't know that you would be doing yourself any favors by trying to score higher on the COMPASS than you would right now. Yes, you might get placed in a lower level math class than you'd like, and that would mean paying to take a remedial math class. However, if you are placed higher than you are really ready for, you will most likely struggle because there will be concepts that you either do not remember or do not have the background for.
Several of my students have said that they were initially very disappointed by their placement, but after taking the class feel so much more confident about math.
Personally, I would recommend you take the exam and go with the placement. You will probably learn the material much better that way.