You could be getting a lesser amount in your check if the IRS has not processed your 2020 tax return or if you have not filed one.
You enter your Social Security number, date of birth, street address and ZIP code, then the tool will give you a message about your payment.
Most of those messages will mean that the IRS does not have the information needed to get your payment to you, or, your payment has not yet been processed.
You may be eligible for a check if you “don’t normally file a tax return and don’t receive federal benefits may qualify for these Economic Impact Payments.