Hello,
The command line to check out the source code from the main repository seems to be OK. Note: you need an Internet connection while it is doing this step.
At this point, if you have not sorted your problem since, I recommend you download the latest installer. It will create short-cuts on your desk before installing TELEMAC. This short-cuts will enable you to complete the installation manually, with additional error messages, if it fails again.
Hope this helps,
Sébastien.