Sorry to hear that.
IMO, I think your best bet is to retake the DAT. This would be your cheapest option. Don't get me wrong, you've certainly made a vast improvement compared to your first test, but while a 19AA is good, it's not great nor competitive these days. If I were you, I would study extra hard and aim for a 21AA+ (no less than a 19 on each section) to solidify your chances.
Your GPA isn't bad, so I don't see a need for a masters, but if you have the time and money, go for it and ace it...it would only help.
Dental assisting is certainly not needed, and I would only advise this if you want to make some extra money. Otherwise, shadowing and volunteering at dental clinics would get you all the dental experience you need as a pre-dent.
Oh and, make sure your LoRs and PS are stellar.
On a side note, certainly keep your hopes high as you still have several schools left to hear from.
Hope for the best, and prepare for the worst!
Good luck!