I submitted my return but forgot to include net losses of $43 from my 1099-B. Do I need to amend my return?

You should amend.  The IRS might just see the whole sales as a gain and not know your net loss.

Has your 2021 original return been Accepted? You need to wait for it to fully process and you get the first refund. Then you can Amend. So it might be a long wait. And it's too early. The Amended 1040X return is scheduled for March 17, 2022.

How to Amend
https://ttlc.intuit.com/community/amending/help/how-to-amend-change-or-correct-a-return-you-already-filed/00/25588

Yes, you'll need to amend your tax return for the form1099-B $43 net losses not reported on your income tax return. 

• For additional information, see Do I need to amend? The IRS gets the 1099-B form from your financial institution and will be looking for it on your income tax return. If they don't see it, you most likely will get a letter from the IRS.

 The amended form 1040-X has not been finalized. Our goal is to provide you with the most accurate information possible. As part of this process, we communicate often with the taxing agencies.

• For up-to-date status, please see IRS forms availability table for TurboTax individual (personal) tax products

 Note: You may also need to amend your state income tax return if you live in a state that has an income tax return. See I need to amend my state return. 

• For the status of state forms, please see State forms availability table for TurboTax individual (personal) tax products

Related information: 

• How to amend (change or correct) a return you've already filed