Spark Notes are there for a reason and they're an excellent tool to aid in your understanding. If, for any reason, your teacher is discouraging you from using them then they're just being plain silly. But I will deign to go with the flow here and suggest that reading the book in the first instance is greatly preferable to simply tossing it to one side and leeching from the notes; the notes are there to bolster your pre-existing understanding, not develop it from scratch and if you haven't even read the book then you'll find that most of it doesn't make a great deal of sense in any case. If you've done the work required of you before you use the notes, then it's not cheating; extra understanding is never a bad thing with regards to situations like this.
Remember, most of the time the stuff you learn in English class is abject BS; your opinion is not yours, it's what your teacher and the exam board want you to think, and you'll likely find that your "opinion" is wrong in an exam even when requested. I remember the old Standard Grade English papers I used to sit at school, there'd be questions like "What do you think the author is trying to achieve....", "What's your opinion on...." and it was a right-or-wrong answer with marks attached. If your opinion, regardless of its validity, didn't match the marking scheme then it was completely wrong and scored zero, regardless of the justification and validity of it. This isn't so true in essay questions at a higher level, but be wary of it.
I'd say "fuck it" and learn the book for your own ends. Literature is there to be enjoyed and treasured, not lectured with a skewed view from some teacher.