With that much light 2 bbs of CO2 isn't going to be nearly enough for that size tank. I suspect it will take at least twice that bubble rate.
You should be seeking a lot more plants if you only have a couple of stem plants. If you can do it, starting the carpet plants with the dry start method would work best. If you can't do that, get a lot of stem plants and plan to get rid of some of them as the carpet plants start spreading out.