Well it's hard to tell without the CM listed. But if you said there was some EWCM around the day, then that's a big indication. What kind of CM were you having on CD 17?
Do you take your temperature at the same time everyday? Before you even get out of bed? That was a big mistake I was making at first... I didn't know you had to take the temperature before you even got out of bed.
I've found that my first chart was basically just a practice run. Temps all over the place because I wasn't doing it right... didn't know how to check my CM or CP (still getting used to that one), etc. I needed a whole cycle to figure all that out. Maybe practice is all you need.

Right now my only advice is that 'only time can tell'. If you're certain that you O'ed on CD 13, you can override their cross-hairs.