Is there anything incumbent upon me for forgetting to pray the two rak'ahs after the Sa'y at Maqam Ibrahim during 'Umrah?

If you have entered into the state of Ihram from the Miqat, performed Tawaf, and Sa'i, then shaved or shortened your hair, your 'Umrah is complete. There are no two Rak'ahs after Sa'i. Rather, the two Rak'ahs are behind Maqam Ibrahim after Tawaf, and they are a Sunnah that may be performed anywhere.