When you clone a repo with git, you get the repo's full history, from the first commit to the last, however, since you made a shallow clone, you only have the history depth that you specified.
If you know which commit you want to go back to, you could try git reset --hard _commit_
to revert your HEAD, the Index and the contents of your working directory to what they were in that specific commit (the first one, in this case).
If you don't remember which one it is, just use git log
to check through the commits for the one you're looking for.
git log commit c09ea7f2a7f01921fda4ee0b53934cba42fb9ee3 Author: That guy Date: The other day This was your first commit
Remember that you only need the first few characters of the commit ID to reset so using:
git reset --hard c09ea7f2a7f019
Should be enough to identify the commit as unique and reset your HEAD, Index and directory contents to how they were in that commit.