It's okay, a lot of English-speakers use them as synonyms, so it can be confusing. ^^; Sex refers to physical characteristics; gender refers to identity. (Basically, the difference between someone being female, and being a woman.)

Haha, don't worry about leaving comments on every chapter :) As long as you're enjoying it, it's all good. (I totally hear you about the kanji. I'm terrible at them, too XD)