Even if I might be called over-diligent, I had been keeping a record of expenses in preparation for this time.
「この時に備えてマメと言われても支出の記録をつけてた」＝＞
"Even if I might be called over-diligent, I had been keeping a record of expenses in preparation for this time."
この時に備えて = in preparation for this time.
まめ ＝ diligent, conscientious
支出の記録 = a record of expenses; a record of expenditure
「予想以上にお金の減りが早く驚いたが支出記録を辿ると合点がいった。」＝＞
"I was shocked at how much faster than expected the money (in my account) was going down, but when I followed up by looking at the record of expenses I understood."
アメリカ合衆国 
