Since they're young, it shouldn't be too much of a problem, but they won't take off like you want them to. Once you get that MH though, your grow you progress a lot faster. You can always add a small oscillating fan, which you should anyway, which will help to remove the hot air around the bulbs and disperse it throughout the room.

Also, that looks like aluminum foil, which you should lose because it actually absorbs a lot of light. Flat white paint is your best bet since you seem to be on a budget. And don't use mirrors; they absorb light as it passes through the glass twice, and they create hotspots.