I know there have been many errors in amounts reported on this first wave of payments that went out. Some received less than expected/due and others actually receiving more than expected/due. If you are sure that your income is within the range to receive the full amount, I would contact the IRS - but please note that it is going to be very difficult right now to get any resolve. Some folks have reported much better luck with contacting a local IRS branch within your home State - selecting the option to make an in person appointment and then actually getting a human being on the phone.
Here is a link to some really helpful information as well:
3rd Stimulus Payment - What Might Hold Up, Delay, or Reduce What You Receive