I'm a Journeyman/Red Seal welder and I managed to fail the practical the first go. I also didn't follow the instructions and circled more than one fault on my samples. I asked the lady at the front desk what I should do if I find more than one, her reply was "pick the most obvious". It is a fairly easy test, if you see a fault right away that's the one you should mark down. Once you identify it measure it and compare it to the generic welding standard they give you and either accept or reject the sample making sure to mark down the size of fault you observed.
What problem with measuring are you having? The easiest way if you haven't had any training in inspection tools is look up youtube videos. There's several available that show you how to use the gauges provided for the exam. (Vwac, fillet, bridge cam, hi lo and a basic ruler.)