Honestly, the odds are not in your favor. However, to optimize your chances of getting the best score possible, I'd keep the following in mind:
1) Taking practice tests is a useful way to work on stress and time management, but it's no replacement for studying. I'd cut your number of tests in half and spend more time reviewing and understanding your performance on each test (and of course, just plain studying).
2) Strive for balance. DS is 40% of your quant, so if you have a huge weakness there it's worth pushing, but you need to be doing at least okay on every major topic. Create balanced study sessions that hit multiple topics/question formats.
3) Master timing. If your timing is not good, nothing else really matters. If that 420 score represents a timeout, pledge to yourself that you will
never time out again. If you work with timing benchmarks, that's a perfectly achievable goal.
4) On test day, aim to match your highest home score. Seriously. If your highest score is a 510, tell yourself "Hopefully, I'll score around a 510 today." The point is to do what is working and not try to change your practices on test day. People who try to beat their best home score tend to end up with alarmingly *low* scores.
Good luck!