I honestly don't know how GitLab works, I use GitHub, but check if the repo is marked as private.
I had similar issue on GitHub where my friend couldnt retrieve and clone my repo even though he had a status of "Contributor" cz I accidentaly checked it to be Private. Also check if your GitLab account and one you are using in your Command line tool is matching.
Today, I was having the same issue. The repo was working fine at my home machine, but when I tried the same repo in other machine I started facing the same error. I was using below URL
If still you get the error, then Remove remote origin by the following and retry again by adding the origin using the correct command.
to remove origin - git remote remove origin