You reported your income twice: once on  F1065 and again on F1040 Schedule C  and you ask if you should Just Not Worry About It ??        Sure - don't worry about it.

Edit:  I missed the 'extension' in the question.  So only reported income once?   However, you can't ignore filing a 1065 return if IRS is expecting one.   CP575A letter indicates what type of return IRS expects to be filed for the EIN issued.  

If you filed an unneeded extension just let it expire.

Yeah, I only reported it on the Schedule C. I realized later I didn’t need to file a 1065 because I am the sole owner of my LLC. I wasn’t sure at the time so I filed to extension incase I needed to go that way.