Change to Freestyle?

I am 29 and started to swimm few months ago. I learned breaststroke only and I swim 50m between 1:00 and 1:10m (from pool edge, no jump). In 5 weeks there is an amateur open water 1km contest. I swimm 1km in 22 minutes. I've been told thats absolutely fine for the contest, but there are faster swimmers of course, since most people will swimm freestyle. So i started with freestyle few days ago, but i am slower and have less endurance at the moment, then with breaststroke. Does it make sense to work on my freestyle in the time that is left or should i continue to work on my breaststroke? (just discovered the 'The Breaststroke Lane' thread here :) ) Right now I swimm 3 days per week, each 2km breaststroke, but I am willing to train 4-5 times per week.