Thomas Ray

This is perfect

Alright. So, I'm going to unload everything I'm thinking about this right now, and I really really hope it's not too much.
Basically, it all happened really quickly. That's not necessarily bad in this context, seeing as it's all in chats, or texts, or emails, and there's always time between those. Anyway, they are in the same science class, s they're bound to see each other and talk to each other (or at least I hope so because relationships that take place entirely online are not usually healthy, and can lead to many kinds of issues, such as stalking, unrealistic expectations, idealized mental pictures of either party, etc... In under three minutes of reading time, they're using the word "love" to describe their relationship, even though we don't know of any times they've met each other in person other than seeing each other at school. You could maybe have them reference a time they met somewhere, or throw in a school project that they need to text about, anything that shows they're getting to know each other away from their phones. That would make their friendship better, and more realistic.
I always want to be in character's heads, which makes this format of writing not quite my favorite but done right, I like basically anything. So what can be done better? I have several opinions that you definitely don't have to follow. And if you're not interested in editing this story, by all means, don't. It's all up to you.
First of all, as I said before, they don't have much time to get to know each other very well. This could be fixed by either making the story longer, and having more text messages, or by making the story only part messages and actually show them in their everyday lives, as people--but that is a really extreme option, so... You could even just put dates and/or times to show when each text came in, and anyone who reads them and does the math will be able to see how much time is going by. They could have another outlet of communication, for example, emails where they send longer things about their interests, fandoms and favorite things in general. They could talk about deeper things as well as surface-level things, and ask each other questions. basically, learn about each other. I think that would be really fun to read. You could just hop back and forth from longer email to trivial text, then you could have the emails get shorter as they run out of things to say, then they could rely on their texts more as their interactions become more scarce and the anxiety of wondering if they don't want to talk to you, or if you said something wrong.... that could be shown through texts.
If either of them had, say, family problems, that could be an interesting topic of discussion, and would create opportunities to show how the characters deal with different situations.
All we're really seeing here are two teens infatuated with each other, and since there don't seem to be any obstacles between them except for Clara's doubt, their worrying feels a little melodramatic. That's not to say the story is bad, I actually really like Clara, and Jack's enthusiasm makes him fun, too. I just want to see those parts of them affect parts of their lives other than their romantic one. e.g, Clara's self-doubt makes her already existing friendships shaky, and that causes more stress for her, and Jack showing that he doesn't always have to be enthusiastic when talking to her could help them grow closer together.
There's so much you can do to this, and again, you don't have to, but if you decide to, I'll be glad to help along the way.
There's lots of potential here, and if you want, I could recommend some published books that have similar formatting. they might help to get your ideas growing.

I can't really tell how long they've known each other for... "love", already?

I think if I was in her situation, I would be less of the "nobody likes me" and more of "you don't even know me."
But I don't know this character very well yet, and we aren't in her head, so there's some ammount of mystery in regards to what she actually feels.
I'm going to read the next part now.

It doesn't have to rhyme. It's cute as is.

Sorry for the four stars.... I really like the mood of this poem, it matches my mood right now.

The only thing I don't really like about this is the stealing diapers part. There wasn't really a precedent for that, and I guess I could have missed something..... It just doesn't share the dream-like memory aesthetic the rest of this has. I love the last two paragraphs, though. They bring everything full circle, and that's awesome.