Hi, Popfizz731!
Aah, I'm sorry to hear about your difficulties ><; I'm not that familiar with MacBook and I've used Winrar for a long time (practically the only software I know which can be used to compress files), so...
Can I suggest you borrow your friend's laptop maybe? I think you can only open winrar with Windows. After that, you can copy the content to your USB/HDD. I'm afraid that's all I can think of x_x;