It's were. Here's why:
When a verb
• indicates a wish (Examples: I wish I were home. She wished the store were open.)
• begins with if and expresses a condition that does not exist (Examples: If I were queen, you would bow. If we were any luckier, we'd be rich.) <--this is your example
• begins with as if or as though (Examples: She ran as if she were on fire. They bought stock as though investing were risk free.)
• begins with that and expresses a demand, request, requirement, or suggestion (Examples: The college requires that incoming students register in person. Lucille asks that Tom arrive early.)
that's subjunctive mood.
The present tense of subjunctive uses the base form of the verb. (That means the verb’s basic form: come, arrive, run, swing, think, etc.) The past tense uses the indicative mood except for be, which uses were for all subjects, singular and plural.
Maryn, dimly remembering subjunctive from Latin, where she learned most of her English