As I explained in class there are certain contexts where "were" is used instead of "was". Actually, "was" is ungrammatical in these cases although natives do not usually know it. It has to do with the subjunctive mood.
Check it out:
Subjunctive
More on the subjunctive

Hey guys, Here´s the slideshow we are revising in class. I hope you find it useful.

P from Esther M