Matey, you didn't make any mistakes.
If what you relate is how it happened, that instructor should be banned from taking the lift, let alone flying an aircraft.
All the mistakes were his. You were all rather fortunate he didn't end up pranging you all. It's seriously bad airmanship, (not to mention illegal, I think) to deliberately enter IMC without a functioning vacuum pump, or other vital equipment for IFR flight. To compound it by offering you a seriously inadequate briefing about partial panel instrument flight (which would usually be two or more fully briefed, separate lessons, conducted in VMC) and to then faff around with an ipad...frankly it's beyond belief. (But I do believe you.)
I would be extremely surprised if you were to have a repeat type of flight to that one. I'm not at all surprised you're a bit nervous about flying as a result from it.