I got everything right the first time except for the last move Qb2.

why not b7?

I did Qb4, lol same thing though =)

Because that trades 2 brilliant pawns for an idiotic bishop

after b7??? the line will be

b7 BXb7, aXb7 QXb7, black is back to the game

but Qb2 not Qb4 because if it make the line

Qb2! BXa6, BXa6 QXa6, b7! now black can not dtop this pown with out losing his Queen and he can not play Qa1+ because our queen in b2 QXa1

if the queen in b4 squar it cannot prevent mate in a1 ....... Qa1+#

that is whay Qb2 is a very good move

yes great end game