June is still a ways away, but yes, you should be concerned.
50% of your score is based on math. You can get a good score on test day with super high verbal and so-so math, but it's almost impossible to hit 700+ without high scores in both sections.
Without knowing more about you, it's tough to make an exact recommendation about what you should do. However, a prep course could really help you focus and build the skills you need for test day. 420 to 700 is a huge jump, however, and there's no guarantee that even with a prep course you'll hit that target (or get within 100 points of it) in 2 months, especially if your aptitude for math matches your current skill level.
If you're not under deadline pressure, I'd advise taking a once-a-week course and giving yourself a solid month after the course ends to build on what you learn. Make sure you have ample time to practice outside of class - the classes are the core of any course, but it's in practice that you'll apply what you've learned and become a GMAT expert.
If you are under deadline pressure, then I'd look for a course that's a bit more compact - but certainly not more than twice a week. One can't cram for the GMAT, one has to prepare over time. If you're working full time even twice a week is a stretch as far as having time to really practice what you learn.
Since you're in Boston, you'll have many course options. Of course, I'm going to recommend Kaplan, but talk to peers and see what courses they've taken and what results they've gotten.
