With the decent weather at the moment and the summer getting in to the swing of things you should get a fairly nice amount of bud.
They have at least 3 weeks to go as you said, i personally wouldn't be surprised if you could let them go 4-5 looking at them right now.
Look on the bright side, they are producing, haven't died and if you get some more seeds now you can have a second crop that would inevitably do better.
What medium are you using, any nutes?
-herb