I totally do NOT think the 35/37,000 issue is a blooper. I always took that as David giving her a little extra so he could continue to perpetuate the lie that he "found" the money in that bank account. I mean if he had just given her the EXACT amount she needed, she would have to be suspicious that he just HAPPENED to find the exact amount she needed at exactly the time she needed it. I always thought he was covering up HOW MUCH he cared about her by making the money looked like happy accident, and not the act of the a man in love.
I agree that it would make sense for David to give her more to avoid suspicion, but then why does Maddie say that David gave her $35,000 when Navarone asks how much money is left? "Not a syllable, not a word"