It will heat up plenty, but you will want to run a small space heater in there during 'night' to avoid dewfall and a temp difference of more than 15 degrees.
I flower in the same sized space but run a K plus a 400 HPS in there. You really want a 1000 for that room, especially vegging under a 600 MH. I'd veg under a 400 with the plants all close together and then spread them out to fill the room and flower under a 1000. You want up to 3x the watts in flower that you had been using in veg to be most efficient.