Correct. TW p.50:
"A ’Mech may attempt to stand even if missing one leg, or one arm and one leg, or both arms, but can never stand if missing all its legs. A ’Mech missing one leg and both arms cannot attempt to stand."
There is no additional penalty inflicted.
Of course, if all players agree, the advanced rule from Tactical Operations (2nd Printing), p. 24 "Attempting to stand" may be used.