18 Days in August - Where to go?

We are from the UK and are doing are first road trip in August.We have 18 days but 3 of those are in New York city.
The rest of the trip includes Pennsylvania,Maryland,West Virginia,Virginia,North Carolina,Tennesee.We are visiting various
places in these states but are following the Appalachian mountains,the blue ridge parkway,skyline drive,
visiting places like Gettysburg, Harpers ferry,Roanoke,Blowing Rock,Little Switzerland,Nashvile and Memphis plus others
,then back to New York through Kentucky.
When we leave Memphis we will have 6 days to get back to New york city,but we are not so bothered about stopping as much
on the way back as the way there when we have 9 days.
Do you think this is too ambitious for the time we have.Your help would be really appreciated.

Welcome to the RoadTrip America forum!

I don't see this as being overly ambitious or unreasonable. It looks like you have a good idea of the places that you want to see on your way, as well.