Is there a big difference between my raw scores and official scores?

This is a good question that has two different answers. Let's look at each one!

The difference between raw scores and scaled scores

While you can estimate a scaled score from a raw score, there is not a 1-to-1 correspondence. For example, if you have 20/40 on quant, this does not guarantee that your scaled score will be 130 + 20 = 150 points. ETS says: 

"The equating process accounts for minor variations in difficulty among the different test editions as well as the differences in difficulty introduced by the section-level adaptation. Thus a given scaled score for a particular measure reflects the same level of performance regardless of which second section was selected and when the test was taken."

By taking difficulty into account in the process, this means that they also introduce hidden analysis into the creation of the score. So while a raw 20/40 gives us some insight, it is better to estimate a 10 point range from approximately 145 to 155. 

The difference between projected scaled scores (at the end of the test) and the real scores

The difference was usually much greater when the test first came out, since ETS wasn't sure exactly what the score distribution on the revised GRE would be. But now they've had time to collect plenty of data on student performance, which means there should not be a big difference (if there's even one at all) between the score you saw at the end of your exam and the one you'll see on the official score report, aside from the added AWA score.

Hopefully that helps, and let us know if you have any other questions about this. :) We know the scores are the most important part of this whole process, after all!