My DE Speedy is over a year and a half old, carried at least two days a week, not babied at all and still looks brand new. I'd take it back and ask them to fix it for free or maybe they will even replace it since it's only been a few weeks.
I have a LAMB in a similar size/shape to a Speedy and it got a loose thread like this (but that was after over six months of daily use) - a week later the whole side had unravelled and I had to get the zipper restitched.