Reflectivity of light in a grow op generally requires a suitable sized grow op. Yours is more or less a hobby sized grow. While white walls or mylar are really nice, I'd focus more on the extra / better wattage lights.......a mixture of cfls n a 150 watt hps
Honestly, you can fit a 1000w HPS lamp in there. They cover a 4x4' area. Maybe another 400w just for fun next to it.well my grow room isnt tha big is like 6ft tall n 4 ft wide what watt u think can cover that