| [18F] finally got into my first relationship [18F]... so why do my feelings suddenly feel weaker?

I’m 18F, and this is my first relationship ever. My girlfriend is 18F, and we’ve only been together for about a week.
I’ve rarely had crushes in my life, and when I did, they were usually just based on someone’s looks. This relationship feels completely different. I’ve also always struggled to tell the difference between romantic and platonic love, so I’ve never been very confident in understanding my own feelings.
I’ve known my girlfriend for around 7 years, and we’ve become incredibly close friends. Over time, I developed really strong feelings for her. Before we got together, I was constantly thinking about her, checking my phone hoping she’d text me, getting butterflies over the smallest things, obsessing over her.. and convincing myself she probably didn’t feel the same way. Eventually I confessed because I felt like I had nothing to lose, and she told me she’d liked me for a long time too.
Now that we’re finally together, something has changed. The overwhelming butterflies and constant excitement have become much quieter. It’s only been a week, but it’s making me panic because I feel guilty for not feeling as intensely as I did before.
The confusing part is that I still care about her deeply. I genuinely enjoy talking to her, I look forward to spending time with her, I don’t want to lose her, and I definitely don’t want to hurt her. It’s just that the intensity I felt while I was crushing on her isn’t there in the same way anymore. I feel like now its just something so awkward.
I’m wondering if this is a normal adjustment. Could all the uncertainty and anxiety before we started dating have made my emotions feel stronger, and now that I know she loves me back, my brain has calmed down? Or should I be worried that my feelings are disappearing?
I’m mainly looking for advice from people who have experienced something similar, especially if this was your first relationship. Did your feelings become calmer after you started dating? How did you know the difference between the end of the “crush” phase and actually losing feelings?

TLDR: First relationship (together for one week) after knowing my girlfriend for 7 years. Before dating I had incredibly intense feelings and butterflies. Now those feelings are much calmer, even though I still care about her deeply and enjoy being with her. Is this a normal adjustment, or is it something I should be concerned about?