I forgot to add an account (at loss) on my 1099B. I've already filed my Federal and state taxes. Can I just roll this over to next year?

You can not.  Trades must be reported in the year executed.

You probably should amend

How to Amend (Change or Correct) a Return You Already Filed
http://turbotax.intuit.com/support/iq/Amend-a-Return/How-to-Amend--Change-or-Correct--a-Return-You-A...

You can always not amend of course.  If the IRS never picks up on the "missing" 1099-B then you simply lose the deduction you're entitled to from a security loss.  If the IRS does pick up on the missing 1099-B then you can either agree to pay the tax, (if the basis isn't reported they'll tax you on the proceeds), or amend at that time.

Tom Young

So I added the short term losses (1099-B) that I missed, but my Federal and State returns are not showing any deduction at all. I have already received my Federal and State refunds, if this matters - I had overpaid on both in 2016. I do have other 1099-Bs that WERE included in the original filing, and they did affect my returns. Am I missing something here?

You cannot report trades in the year they were made. You report them in the following year, along with any other income you made that year. Trades made in January 2024 won’t be reported till anywhere from January until mid April 2025.