I promise you this, as another has already mentioned, there is RARELY a time when any pilot does NOT think about whether or not they'll be able to stay in the cockpit. What gets certain pilots in and, more importantly, KEEPS them in is the motivation and determination to not let yourself give up.
Even us in the military wonder every now and then about what may come tomorrow that might kick us out of our dream. Whether it be a bad medical, bad checkride, or decommissioned aircraft, the thought always crosses out minds.
In fact, I think I'd be worried about your arrogance if you DIDN'T question it!
The truth is, you'll see the cockpit of whatever aircraft you want to see if you study hard, pass your exams, and be honest throughout your career.
Good luck to you buddy, on both your life in the wonderful world of aviation and that pain in your stomach about your upcoming checkride. I'm sure you'll do just fine! And if you pass the exam, then you've accomplished what 90% of the pilots out there never have or never will...commercial freedom! Or, commercial slavery, whichever way you see it!