OldDome

I'm doing the second research rotation as part of my program, and it's not going well. I've never felt like such an incompetent idiot.

My first rotation ended up going well in the end, but I asked my advisor if he'd be willing to take me as a PhD student at the end of the year and the response was "I'd have to think about it" which means 'NO!'

I just feel like at the end everyone's going to end up asking why in the hell anyone let me in.

Well you got in so I'd say don't panic. I would ask for more detail about what they calculated it as and how (there could be a mistake if you really think there's no way it should be below their minimum), and what it would mean for you as an incoming student. Would you be on academic probation, etc.?