Am I required to amend if the net is money owed to me?

in the absolute sense No you are not required to file if you are due a refund.  This also assumes the amendment would have no effect on other years.  The issue is that the IRS may have received tax forms reporting those missing investment sales but will not know about those deductions. In that case the IRS is likely to send you a bill and then you'll have to submit an amended return. At that point Turbotax for that year may not be supported, so you would have to do the amended return manually.   so maybe as a minimum you prepare the amended returns but wait to see if you get a notice. Also, do you have a state return that would also be affected by the missing info? 

It would be wise to complete and file the amended tax return.  There is a good possibility that the IRS has received information on the investment sales from the brokerage firm, so would expect to see those sales included on your tax return.

What you are all saying makes sense.  It was actually personally owed physical property/collectibles that I sold privately so the IRS wouldn't know about them.  If I owed, I'd obviously do it, but I also happened to have some deductions I missed so in the end it worked out in my favor.   

@rwom1217 , agreeing with my colleagues @Mike9241  and @DoninGA , I would urge you to recognize the  "private" sales proceeds i.e. amend the return.  I say this because  when you file a return  ( electronically or by mail ) you are  submitting this  as a true account of your incomes ( & allowable deductions ), under penalty of perjury.   IRS may or may not catch the  un-recognized income, but if they do , you will on their watch list for the next three years.  Therefore  and because of  perjury jurat, I will take the trouble of setting records straight.  That is my suggestion -- of  course what you do is  up to you.