Your 720 is a good score.
But, if you want to improve and score even higher you'll need to realize that you have to get ALL the answers correct.
It's not about practicing with harder level questions - doing more 700-800 level questions. No.
It's about being consistently accurate 100% of the time - whether it's EASY, Medium, or Difficult. The difference between a 720 and 770 can be careless mistake on an easy/medium question or on a difficult question - you narrowed it down to 2 choices but chose the wrong one. Choosing the right one in those situations requires an "aha" moment.
Usually students who really break that barrier see that "aha" moment and they realize that "aha" moment gets even bigger after a few more practice sessions. A fundamental change in their way of thinking gets them tackling the Difficult question in a different way.
So, focus on how you're thinking and improving your speed. Don't focus so much on practicing 800 level questions day in and day out - thinking those are the ones that trapped you.