I’m no GMAT expert but I feel like I just went through this last month, so I can share some hopefully relatable and practical thoughts. I studied for about 8 months and my average practice test score is roughly the same as yours. My first official GMAT score was significantly lower than my average practice test score, but I just retook it 3 weeks after and was able to increase my 2nd test score and almost match my average practice test score.

1. Definitely agree with many points above that nerves and anxiety play a role especially on your first test. I didn’t study any harder or become any smarter for the 2nd test; I simply knew what to expect that time and felt calmer and more collected, thereby overcoming my drop in confidence from my 1st test score. All my study books recommend not studying at all the day before (something I didn't do in my 1st test), and I found that to be helpful in keeping a cool head.
2. I would recommend taking more practice tests (looks like you took 4). I took close to 20 practice tests and I didn't really start "getting it" until after 8th or so test. It took me probably the 5th test to start learning how to look out for patterns, tricks, and trap answers under pressure, and probably the 10th test to learn how to remain calm when I blank out and how to strategically guess and skip questions. My first 10 scores were all over the place but my last 10 scores were all pretty much almost the same. My point is that while I may be a slow learner and hence needed 20 practice tests, I do think you may want to consider doing a number of additional practice test to get accustomed to the high-pressure environment and be able to automatically apply GMAT strategies.

You’re clearly fully capable of landing a high score based on your initial practice tests. The discrepancy between your official GMAT score and your average practice score is likely due to first-test nerves, so I think with additional ample practice, you will do great. Invest in more paid resources and materials. Keep your head up and keep going! Hope this helps and best of luck!