When I ran t5no fixtures I used 1x 6700k and 1x 10000k in each fixture, and I had 2 over my 20 long. I found that running only 6700k bulbs made it a bit too yellow for my tastes. Having 2 fixtures should be fine if you're also running paintball co2. Be sure to get some ferts as well.
As far as a baby tear carpet, everything I have seen and read about that plant makes it seem like it needs a good ammount of light, ferts, and co2 in order to make a nice carpet. I would suggest getting another fixture to provide the light, and get ferts for nutrients. Also, if you're patient, I would suggest doing a dry start with it so it fills in faster. You might not even need the second fixture until you add water to the tank, so it can help spread out the cost a bit.