As Greg says, we often replace the subjunctive 'were' with 'was' in informal English. For example, you'll often hear people say "If I was in your situation, I'd ...". This has become so acceptable in everyday contexts that it is no longer considered wrong. I don't know about other examination boards, but a candidate taking a Cambridge exam would not be marked down for using 'was' in this way. In formal contexts, however, we still follow the more traditional rule of using 'were' for the subjunctive. The construction 'If + subject + [be/subjunctive] to + infinitive' is quite formal, so it seems appropriate to use the more "correct" form. But that doesn't mean that 'was' is necessarily wrong - you might well hear this people use 'was' in this context, and it's likely to become more common.

Thanks Su.Ki and Greg

Like Su.Ki says, correct form is 'were'. A lot of native speakers will use 'was', though. I know I have myself sometimes. I'm not sure if this is country specific or 'people' specific. I only mention this so you don't get confused if you hear both forms. :)

It's a hypothetical situation, so the correct form is 'were to'.