I had a very similar experience during a lab internship I took during my biochemistry undergrad degree.

First part of a project was running PCR on a particular plasmid that we were going to use to transfer a gene into Drosophila. But for some reason the PCR didn't work, and I spent almost all of my time trying to get the damn thing to run.

Everyone naturally assumed I was just doing something wrong, being an undergrad with little lab experience. After about ten weeks, it turned out that the lab tech had written up the protocol wrong and I was using the wrong primers. No wonder it didn't work.

Was one of the experiences that made me realise that working in a lab really wasn't for me...