I’d go for job not a good fit, I have used this in the past. My previous job was a short stressful experience for lots of reasons, I’ve been in my current job 8 years with no problems (other than the every day stuff everyone gets) so don’t be discouraged by this one bad experience and try not to call yourself names over it.

As Split says, be prepared to give a more in depth answer if asked. In my case I said it turned out to be more office based than suited me and I wanted a physical job, broadly true but I left out the crackpot manager who bullied me because these things can be misunderstood.