i.e. So let it be if I be guilty. The word is doubled by her as an evidence of her innocency, and ardent desire that God would deal with her according to her desert.
Related Commentaries of Numbers 5:22
Numbers 5:22
22 And this water that causeth the curse shall go into thy bowels, to make thy belly to swell, and thy thigh to rot: And the woman shall say, Amen, amen.