It is perfectly correct and acceptable to say 'was' rather than 'were' in unreal present/future conditionals. The vast majority of people in the UK would say was, and I assume it is similar in other English speaking countries. All modern grammar books state this, and the trend is to teach was as the first alternative. There are even types of conditional, such as the past habitual, where 'was' would be correct and 'were' would be wrong.

Hi, Using “was” instead of “were” in unreal conditionals (the subjunctive) is common in informal speech and writing, especially with I, he, she, it. For example: • If I was you, I’d study more. (informal) • If I were you, I’d study more. (formal, traditional) In formal writing, “were” is preferred and considered correct. In casual conversation, “was” is widely accepted.

Tim gave an excellent answer. Grammar books such as English Grammar in Use by Murphy and Practical English Usage by Swan give “was” as the primary usage.

very common for non-native speakers of course, it's a mistake

Great question! In unreal conditionals (when imagining something contrary to fact), the traditional rule is to use “were” with all subjects — even “I,” “he,” “she,” and “it.” This is called the subjunctive mood. Examples (traditional grammar): If I were rich, I’d travel the world. If she were taller, she could reach the top shelf. So, is “was” incorrect? Not exactly. While “were” is still considered more formal and grammatically standard, especially in writing, “was” is commonly used in informal speech — particularly with “if I was”. Examples (informal usage): If I was rich, I’d travel the world. If he was in your position, he’d do the same.