Excess SEP contribution

I have an excess SEP contribution in 2020, but do not wish to withdraw the excess.  I will only deduct the maximum allowed on my taxes, which is less than the excess.

 

I have read in other forums that if I leave the excess in, I will be subject to a penalty and must reduce the maximum contribution for 2021 by the 2020 excess amount.

 

Is this correct?  If so, what would be the penalty?