You're well on your way now that you've signed up for our GMAT course.
But seriously, you did the right thing by pushing back your application. Without question, you have a MUCH better chance of getting in with a higher score (assuming you get one, of course) in Round 3 than with a 570 in Round 2. People absolutely do get into top MBA programs in Round 3. Yes, it's a bit harder, but not as hard as getting in with a 570. I'll put it another way: Top schools accept far more people in Round 3 than they accept people with sub-600 across all three rounds!
Since you're already 28 years old (unfortunately, approaching "old" in some admissions officers' eyes), I do think it's worth a shot this year. If you don't get in, you can try again in the Fall, and can still be very successful as a re-applicant. Again, that assumed that you do manage to significantly boost your score before R3. I can't give you a magic number that you should aim for, but if you take it again and only boost your score to 600, then I would say wait, spend months on working to get yourself into the high 600s (not easy, I fully understand), and then apply in R1 next year.