Substantially lower score on MGMAT than on GMATPREP PLEASE !

Hi everyone.

Are MGMAT practice tests harder than GmatPrep?

My Scores:

MGMAT 570
GmatPrep 700
MGMAT 600
GmatPrep 680
MGMAT 570

I don't get why there is such a huge discrepancy. I have been studying from OG12 but I rarely see any overlap, and if I do I still have to re-solve the question because I don't remember it. This is really freaking me out. I do feel more comfortable taking the GmatPrep tests I feel more at ease, and when I take the MGMAT tests I feel very anxious and uneasy...(Maybe because I have been getting lower scores idk) Does anyone have any suggestions or know why I may be experiencing this. I feel like the questions on GmatPrep start with easier questions and get harder (as it is supposed to do I think) and the MGMAT gives virtually the same or pretty close level questions throughout. My test is next Friday and I plan to take a practice test on Monday and Wednesday both GmatPrep and I will be reinstalling the software so that I get new questions. I figured it would be best to do the practice I have been performing well on instead of MGMAT to keep my confidence level high.

Has anyone else experienced this? If so, how did you perform on the actually Gmat and which is probably more comparable.

Thanks!