Prevent it rusting further.
WD40 used liberally, then left to run out of the tubes. Careful now, it's inflammable. Reapply twice in a month, a greasy coating of oil builds up as the lighter solvent evaporates. Use it on external frame bits too - but it gets on your clothes.
Don't get it near your brakes or tyres.
You need to have more rust than frame for your bike to snap, methinks.
"A simple and inexpensive way to remove rust from steel surfaces by hand is to rub the steel with aluminium foil dipped in water. "
Ya learn something new everyday, here.