yeah, the two downloads are a bit confusing. Sounds like you flashed the image that runs Umbrel directly from the USB, rather than the installer that puts it on your internal drive.
If you want everything on the internal SSD and no USB left plugged in, you’ll want the USB installer ISO. There’s a walkthrough here. That route does need a screen and keyboard, but only for the installation. Afterwards you can unplug them and access it from your browser.
Just watch out: it wipes the internal drive, and it’s a fresh install, so save anything you need first.
If you’d rather keep booting from USB and only use the internal SSD for apps/data, which umbrelOS version are you on? The current guide says it should ask about internal drives during setup, so that missing step is worth checking.