Do you like my story so far? Pretty short?

You have a good opening and an idea that could make a good book. You do well writing dialogue, too but you need to learn more about using attributions. Sometimes you need "he/she said" but when there are only two people in a conversation you don't need many. Don't use them to try to tell the reader how something was said, only do it when the reader wouldn't know who was talking. Your line, "“And I care because?” is a good example but there are a lot of more places you could do the same. Look for unnecessary lines and cut them like, "I guess I should tell you, her name is Julie." You don't need that because right after you have Josh say, "Sorry, Julie" so we learn her name without you stepping outside the story to tell us. Watch out for repeated words or phrases like "lab partner", "low-cut top" and names (you repeat Tally, a lot) This is a little sensitive, I guess but when you're writing from the view point (what writers call point-of-view or POV) of a boy you have to be careful to make not only his dialogue sound like a guy's but also his thoughts. I'm afraid a guy wouldn't think, "chest" for example. I think you're on your way to something good but it's not an easy thing to do. If you keep at it you'll be a good writer. (There are a lot of typos in this but I figured it was a first draft and those are easier things to fix than bad storytelling and you're doing well at that.) If you have any questions about what I have said or writing in general you're welcome to email me from my profile here on Answer.