As you've discovered, you racked way too early. Please ignore the kit instructions that say to take the beer off the yeast at 7 days. They are outdated.
A good rule of thumb is 10-14 days in primary then rack to your secondary to allow the beer to clear ("drop bright"). Or just keep it in the primary for three or four weeks. The old fears about yeast autolysis are unfounded. After fermentation the yeasts go to work cleaning up after themselves, smoothing out flavors, reducing esters and phenols and just generally making your beer a lot more pleasant to drink. That added time also gives them the leeway to deal with lower fermentation temperatures.
Your FG (final gravity) should have been somewhere around 1.014. If it wasn't, you should have let it sit longer. Patience is critical.
At this point you could brew another, similar, batch of beer at a lower gravity and ferment it with a clean yeast known for strong attenuation, Wyeast 1056/WLP001/US-05 or Nottingham, for example, let it ferment all the way out, and blend the two beers.
I hope one of the more experienced brewers will chime in because I'm trying to figure out why you can't take it off the gas, rack to a carboy, let the CO2 off-gas at room temperature for a couple of days, and hit it with another dose of yeast until it drops to your target FG.