How much was on your 1040 line 30? You better double check your bank statements and check your IRS account (both accounts if married) to see what they sent you. The 3rd Stimulus started coming out in March 2021.
https://www.irs.gov/payments/your-online-account
You should have got 2800 for the 3rd stimulus payment. Maybe even 4200 for you and spouse and dependent based on your 2020 return. Where did you get 2100? Are you going by the letter you got from the IRS? They send a letter to each spouse for half. So 2100+2100 = 4200. Double check your bank account.
