CP2501 for sale of rental property

[Cara Nall]

I sold two rental properties in 2017, and just received a CP2501 claiming a discrepancy on my taxes because two 1099S were reported to them and not on my taxes. I thought I'd entered the sales correctly, using this guidance: 

https://ttlc.intuit.com/community/investments-and-rental-properties/discussion/how-do-i-report-the-sale-of-rental-property/00/510920

And yet I see that there wasn't a place to explicitly put "here is my 1099S and here's the amount listed" so it triggered this audit. Any ideas/suggestions/what I did wrong? I'm allowed to simply submit an amended return, which is my preference instead of pulling together reams of paperwork.