I had very mixed feelings about my skype interview with WUSTL. I would go back and forth between it went okay so-so and I bombed it obsessing over minor details. Ultimately, they thought it went well because they are flying me down to meet the department in person. I wouldn't worry about it too much. It probably went much better than you think it did. After my UCSB interview I was simply puzzled. It went fast and I feel like I didnt say much that was substantial. A week or so later I was admitted into the program. Your probably just over-thinking it. In the off chance you actually bombed it it's too late to worry about it. At this point I would simply sit back, relax and enjoy your intoxicant of choice.