Next time, get the boy away from the background, and get another light to light the background separately. Much easier than having to sort it out in post process.
Cheap continuous lights are a bit useless, really. If the light isn't bright enough, open up the aperture, crank up ISO, or get the light closer to the boy. Or combination of all 3. Getting the light close to the model is the first thing you should do, as it makes the light softer.
But ultimately, I'd flog the light, and get a cheap flash. Continuous light for photography is just not suited unless you spend big money for a decent setup - but for the same money, you can buy an arsenal of good flash system.