There is no bias in one direction or the other. When you look at the aggregated (average) data, it isn't the case that most quant scores go up or down on test day or that most verbal scores go up or down on test day.
Some individuals go up, of course, and some individuals go down, but I have no way of predicting what will happen in your course (or anyone's!).
All I can say is that, in general, whatever you're scoring within a week or two of the real test is most likely around what you will score on the real test.
I am concerned that your GMATPrep is showing such a large difference compared to MPrep - with quant much higher and verbal much lower. Those kinds of score fluctuations usually mean there are issues with timing, mental stamina, careless errors, holes in your foundation, or all of the above. If that's the case, you would want to work out whatever those issues are before you take the real test, ideally.
You can use this to analyze your MGMAT CATs:
https://www.manhattangmat.com/blog/inde ... ts-part-1/GMATPrep doesn't provide you with data, unfortunately, so you'll have to just dive in and figure out how to analyze it qualitatively.
When you've done that, feel free to come back here to tell us what you've figured out, as well as what you think you should do based on that analysis. We'll tell you whether we agree and advise you further. (Note: do share an analysis with us, not just the raw data. Part of getting better is developing your ability to analyze your results - figure out what they mean and what you think you should do about them!)