Is my action correct in not repeating the ablution after remembering to wash a part of the ghusl and washing it?

If someone performing ghusl (definition) to remove major ritual impurity forgets to wash a limb, they only need to wash that limb, and are not required to repeat the entire ghusl. This is because sequence (tartib) and continuity (muwalat) are not conditions for ghusl; rather, continuity is considered a sunnah (definition) by the majority of scholars. What you did is correct, and you are not required to repeat ablution after ghusl for janabah (definition), because minor ritual impurity is subsumed under major ritual impurity, and for someone performing ghusl for janabah, their ghusl suffices for ablution.