When you did that, since a “first” sync on a new device is always a one-way sync, it sounds like you chose to upload your “collection” – which was just this one new deck – to AnkiWeb, and you overwrote your real collection there. That was where you went wrong.
Presumably your regular computer is turned off right now – or at least Anki is closed and not syncing, right? When you get back to your new own computer, you’re going to need to be careful to fix this –
- Start Anki while holding down Shift (until you see the confirmation message), to skip auto-sync. You’ll find that your collection is just like you left it.
- In Tools > Preferences > Syncing, choose “On next sync, force changes in one direction” – and then sync. When given the option, you need to upload to AnkiWeb to put this collection back on AnkiWeb. That new one-deck “collection” on AnkiWeb will be overwritten.
- Then, you can import the new deck into your real collection, and you’ll be able to continue syncing normally.