If my memory serves me right, you still owe me one thousand dollars.
如果我没记错的话，你还欠我一千块钱。
If my memory serves me right, it happened in the summer of 1999.
如果我没记错的话，这件事发生在1999年的夏天。
If my memory serves me right, you told me you would return next month.
如果我没记错的话，你曾说过你下个月就回。