I noticed the same thing on the verbal. I scored much higher on the real test than I did on powerprep. Interestingly enough I got the exact same scores on the real GRE as you did Vladimir.
Just keep studying and doing practice problems. 3 weeks is plenty of time to raise that score to what you want it to be. Like others have said you really need to take your time, especially on the front part of the quant section. When I took the GRE a couple of weeks ago I spent 24 minutes on the first 8 questions. Maybe that's a little too much time but it worked out well for me. I ended up with 790 Q / 720 V.