If you can pass your ACS you will be fine. Make sure you have paperwork like warning notices, AR/ID stickers, CP12 if you do landlord gas safety checks. He will want to see analyser (and calibration cert) temporary earth clamps, manometer, paste etc etc.
He asked me a few questions like talk him through a tightness, how to do a gas rate, what to do in an unsafe situation. Nothing to catch you out.
I didn't have anything to show them when they came out as I only had done a few services and because I had 3 inspections cancelled and left it too late and couldn't get anyone in so he asked a few more questions. They will know within a few minutes if you are just nervous or unable to do the job so just relax have a cup of tea and a chat.
I think the first thing I said to my inspector was "your busy down here seeing all the prosecutions in the gas mag, do you want to pass the customers my numbers and I will sort it"