Hi Oli1324,
Since your GMAT scores are remarkably close to one another, there's something about your Test Day performances that are consistent, but THOSE consistencies are NOT consistent with your practice. Clearly something that you do during practice doesn't "match up" with the reality of Test Day, so we should start with the likely issues.
Since you mentioned 3 practice CAT scores, I'd like to know more about those Tests:
1) Did you take the ENTIRE CAT (including the Essay and IR sections)?
2) Is this the first time you had taken those CATs (or had you taken them before?)?
3) What time of day did you take those CATs and what time of day was your Official GMAT?
As far as your overall studies were concerned:
1) How long did you study (it looks like it could not have been more than about 1.5 months, but was it less than that?)?
2) Were there any other resources you used besides the ones that you listed? Did you use the GMAC CATs and resources?
3) Approximately how much time did you spend studying each week?
Since Most Test Takers spend 3 months (or more) on their studies to hit their respective "peak" scores, it might just be that you haven't put in enough time and practice yet. I think that there might also be some problems with how you studied (since most of what you were doing was self-teaching), so to hit your goal, you might need to learn some new tactics and invest in some new GMAT resources.
GMAT assassins aren't born, they're made,
Rich