Why does the stimulus money increase the amount I owe on my federal return (Tax Year 2020)

why does the stimulus money increase the amount I owe on my federal return.  When I enter the amount of  $1200 then the first stimulus check and $1200 for the second one,  I have to pay example: $350 back to the feds.  when I enter the correct amount of $2400 for the first stimulus check I have to pay  $893 back to the Feds.