I hope I can describe this correctly. Please feel free to ask for clarification.

I went to Chipotle for lunch today (yum!). The parking lot is cramped and poorly laid-out. I pulled into the lot behind a Large Truck, and spotted an empty parking space. This space is notoriously difficult to get into, but since I have a compact car, I can manage it fairly easily. I noticed that Large Truck drove past the space and then stopped; it appeared that Large Truck was waiting for another car to pull out.
So I maneuvered into this spot, and as I was pulling into it, I noticed the Large Truck driver staring at me and giving me a dirty look. I then realized that, with the way Large Truck was positioned, he had probably pulled ahead in order to attempt backing into the space. So essentially, I swung into the space while Large Truck was preparing to back into it, making me a parking spot thief. I was already in the space when I realized that I had probably stolen his parking spot, so I went ahead and parked there, but I felt guilty.
What is the right thing to do in this situation? Should I have vacated the spot when I realized I had stolen it? Am I overthinking this?