Gnosis App operates the cash back program on a weekly basis. The period is between the beginning of Sunday at 12:00 am, and the end of Saturday at 23:59 pm.
All eligible transactions made between these times will be counted. Note that not all purchases with your Gnosis Card are eligible. Check the related articles on this topic.
Cash back is calculated on Tuesday of the next week. If you've tallied your transactions outside of the right weekly time period, that may be the reason why the CRC rewards are different from your calculations. There could be transactions from your last period that haven't cleared yet, and therefore weren't included in your cash back.
Your cash back rate and maximum weekly reward cap are tied directly to your GNO holdings. Higher holdings unlock a higher rate and weekly cap as follows:
0 GNO would allow you to receive a capped amount of 1000 CRC;
From 0 to 0.1 GNO, your cashback ranges from 1,000 up to 2,000 CRC;
From 0.1 to 1 GNO, your cashback ranges from 2,000 up to 3,000 CRC;
From 1 to 10 GNO, your cashback ranges from 3,000 up to 4,000 CRC.