My husband died in Dec. 2017 so I would have filed a joint return, but I was told that I didn't need to file because I didn't owe anything, Was that correct????

Not necessarily.  Whether or not you need to file your tax return with the IRS is related to your filing status and your income level.  Look at the charts on pages 10 - 12 on the IRS 1040 instructions attached below to determine whether you need to file or not.

https://www.irs.gov/pub/irs-pdf/i1040gi.pdf