If I were you, I'd say: Were I not far away from your, I would attend your class. I think this is the best choice.

No, the word 'if,' has nothing specifically to do with the subjunctive in English. The sentence that you have written (your second one) is a conditional one, rather than a subjunctive one. 'If,' is commonly used in conditional sentences. The subjunctive is used to make suggestions, give advice and show urgency. For example, the following sentence uses the subjunctive: 'It is suggested that he urgently see a doctor.' Your second sentence is okay. The first does not make sense. You could say: 'I intended to come to your class, but I am still some way away, and it does not look as though I will make it in time.'

I think you've confused us by using grammar jargon. ;) I agree with some parts of Andrew's explanation - yes, the use of "if" is not specifically subjunctive. The links offered are for Present Simple Subjunctive, but second conditional uses Past Subjunctive. We typically use "If X were..." for past subjunctive, but using "was" is also becoming common. If I were you, I would still use "were". In a conditional sentence, you may use "if". Not all conditional sentences use subjunctive mood. You can have a closer look here, though there is much more to learn about this part of English: https://en.wikipedia.org/wiki/English_subjunctive

well, as you know the first sentence is somehow different to the second one 'coz the first one meant first of all intend or decide to attend your class then you think that you might not get there in time due to long distance away form your class. This sentence indicate generalization. the second one indicate condition type II, so how to use condition type II? well, The conditional is usually used for imaginary situation in the present. "If I was not so far away from you , I would attend your class" and the meaning is I am not far away from you so I will attend your class another example, If I knew you were back from your holiday, I would phone you. the meaning is I don't know you were back from your holiday so I don't phone you. my example is a bit weird, It's better off I use the sentence in conditional type III. "If I had know you were back from your holiday, I would have phoned you" and the meaning is I didn't know you were back from your holiday so I didn't phone you. If you have any questions feel free to ask me your best, George Woolard