Setting profile name preventing me from launching game (since purchase)

I just purchased the game and am having issues with being able to launch Minecraft Java. I didn’t realize clicking on the PLAY button would ask me to set my username, so I went to the dropdown menu that sends you to your Java Edition profile. I set my username there, and when I went back to click play, it then asked me to set my username. I tried the one I set on the website, but it said it was taken (since I had already set it on the web). I added an underscore to the name and it said it was clear, but I suddenly got an error message when I tried to continue. I’m assuming when I set my username on the website before, it locked me out of being able to set my username normally and the 30 day cooldown is preventing something from letting the launcher set my profile and log me in, preventing me from being able to play. I’m not sure if that makes sense, but yeah. It’s pretty stupid, I know, but I’m writing this so no one else might have to experience the same thing.