ahhkk!
aluminum foil is terrible! it causes hotspots and it's so flimsy.
just get a some mylar or some flat white matte finish paint and paint the walls.
your light is a CFL, and if you've only got one, i suggest you run out to lowe's or home depot and get a 3 pack for like.. 15 $ .. maybe 5$ i can't remember.
the point is, they are cheap and you need alot, especially if that's all you plan on using the ENTIRE grow.
i'd get TONS of them. cover the entire room, make it a tanning bed.
and then get that flat white finish man!
do you know what type of soil you're using or anything?
strains? pics?