I suggest you call her and tell her you rechecked your old notes and found that you had only quoted her the $150.
...OR, you could call her and tell her you rechecked you old notes and found that you had quoted her $250. Think of it as 'payback' for years of MUSICIAN ABUSE at the hands of those who hire us

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Of course I'm kidding but my feelings on the matter align perfectly with Mirza's.
chas