Don't panic. You should file an amended return, but it won't change your refund.

Duke did a 1:3 reverse stock split before merging with Progress. The Cash in Lieu transaction is normal for the liquidation of a partial share.

A partial share has a cost basis. You can determine the cost basis for the partial share, or if you don't have the patience use a cost basis of $0.

Wait for the IRS to process your return and refund. Your carry over loss will offset any possible gain. File an amended return after your refund has been processed.

If the IRS catches the inconsistency while processing your refund, they will send you a correction statement.