If you could go 100% for 17 minutes and ride another 60 miles, you didn't go 100%. Probably not even 90%. If you have never raced, your RPE meter isn't calibrated for racing, where going 100% is mandatory but has to be managed. This will come with time and experience. I will also say that doing a test on flat ground is harder than on a steady grade. The hill provides an erg type effect that flat ground doesn't. It's harder to maintain steady power as the flat road undulates.
Do your test. In the meantime go ahead and set up your zones using your ride data. If you start doing intervals and you are not challenged to complete them, then bump the zone up until the test. If you are challenged by your intervals then you are in the ballpark.