7 Corps total. The Union had 50,000 men in reserve. Lee had zero.
lee had three corps of 30,000 each(approx)
You are misunderstang what happened. On July 3rd at 3:00 PM the Union forces on Cemetary Ridge numbered about 10,000 plus arty( a lot of it) and a little cavalry. The CSA attackers outnumbered the defenders 3:2 ratio. The Union line would have broke if the CSA cavalry had been there to support the flanks of the attack.