If you have the whole summer to finish this, kudos to you for starting now.
I would actually take a break from the assignment that you are currently struggling with. I sometimes find that it helps to let it rest for a day or two and then come back to it, and you do have time to do that. When you come back, I would read the whole essay first, and then start breaking down individual paragraphs. If you understand the whole thing as a gestalt, it may be easier to summarize the parts.
Good luck! I wish I'd had assignments that interesting for high school English.
