Apprentice of 4 months, about to start a full week on call.

So I've been with a small home heating company for about 4 months now. I am relatively confident with oil fired units, I would say I've replaced or repaired 90% of the parts on various models of furnaces. Boilers I also can clean and service with little to no guidance. I start my first on call week in 14 days and I've never been more anxious. I know I will do just fine and my service team has told me on numerous occasions that they are a phone call away. I still feel like the "new guy" and that I don't know what im doing during an install. Please she's some guidance for a new, anxious, but motivated tech to dull this helplessness.