Answer:
Yes, you would have to go back to Ve’al Ha’kol, and to say Boneh Yerushalayim again.
Sources:
Although the Aruch HaShulchan (188) discusses the question of changing the order of the berachos in Birkas HaMazon, and writes that the order is not me’akev, Shut Tzitz Eliezer (13:16) cites from many authorities that the order of the berachos is essential and me’akev, so that you would have to return to the Ve’al Ha’kol and continue from there.
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