Hey Casual Warrior,
You should certainly keep up the sprint intervals. I did a post on my site about how Interval Training improves endurance better than endurance exercise. It is based on a recent scientific study...
That being said...you will need to do some distance work to prepare your bones and body for the extended effort of your race.
Also...one of the readers of my site made a great point about this study:
"If someone wanted to improve their 5 mile jog time, then they should practice jogging 5 miles. If someone wants to increase their VO2 max, then yeah, intervals are great. I can assure you that endurance track athletes do not spend more time doing intervals than they do endurance-style training. Up until a few years ago, people used VO2 max to measure a person's endurance…but that line of thought has been discarded."
So you still have to do some distance work.
Hope that helps!