Normal atmospheric conditions on left. Oxygen rich flask on right.
When thinking about the steel wool lab it is important to think very logically and trust your observations.
If your lab technique was good, and you didn't knock off too many crumbs from the steel wool ball, your experiment should have gained mass. How is this possible? Remember chemically combustion is combining with oxygen (O2 molecules). So instead of simply having iron atoms, we know have iron oxide molecules. Oxygen has mass, so if we didn't lose any iron, the experiment has to gain mass.
Fe + O2 ==> ? + energy release (That gives off the glow)
The diagram below is a somewhat complicated phase diagram that shows under atmospheric conditions where oxygen is present in excess, the stable form of iron is Fe3+ ion.
So the reaction becomes
Fe + O2 ==> Fe+3O-2 + energy
Now just criss-cross for the proper compound formula and then balance the equation. Remember no subscript on the iron, and oxygen is a diatomic molecule.