What you see on SDN is a small sample size. The ones you hear are the great success stories. There are many who score average, that is why it's an average and below so don't feel too disheartened. This applies to the real DAT and the practice exams. Scoring over 19 which is the average should give you a decent chance if you have a competitive GPA, that said you still want to perform your best to give yourself an greater chance. Most people study for about 2 month. Watch Chad's video, Youtube vids on topics you do not really understand and learn that way? Do not keep focusing on the questions and topics you find comfortable, instead focus on the ones that you do not really like but can still tolerate learn it 🙂 Ochem roadmap in the DAT destroyer (located in the back when I had it) helped me out tremendously. I committed it to memory and applied it to questions. For chem, I just kept doing problems and committed the equations to memory. The hardest part was recalling what equation to use. I just wrote down all the given variables and bleed my brain dry thinking of how to set the equation up and if it is similar to an equation I memorize during my studies. while Remember between all the studying to take a break and relax your mind so you can comeback with a different perspective.
Good luck and stay positive.