You don’t reference your source of how to do this, but this isn’t the typical way I am familiar with. I’ll put mine at the bottom in case anyone stumbling on this could benefit from them.
Did you have a look at here or here in regards to the way you seem to be trying?
Is that your actual tunnel command or do you usually have a space after the -L? I don’t know if a space being absent matters.
Running Jupyter notebook on a remote machine resources: