It sounds like guy 2, though a lot depends on how many months' data gave you the calculation that you have 26-day cycles. If this is from months and months of records, that's good. If you haven't used the app very long, it's not as useful.
If you can get an appointment sooner than August 23, do it. (You might try calling them and saying you'll take a cancellation.) What you're after is to get an ultrasound scan at that appointment, and this next week would be better than the week after.