I feel like I am highlighting every other sentence

So I am reading the first volume to Tearmoon. I am really enjoying the book, but I find myself highlighting 2 to 3 sentences per page. Either sentences I don't fully understand or sentences I want to be able to recall the grammar.

I figure the more I read the series, the more I will better understand the grammar and sentences. Should I just keep going or move to a different book? I feel like this book is just right for my level despite not understanding some parts.