Simplify the PATH first.
In a CMD, type:
set PATH=C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\WINDOWS\System32\WindowsPowerShell\v1.0\
set GH=C:\path\to\Git\2.13
set PATH=%GH%\bin;%GH%\usr\bin;%GH%\mingw64\bin;%PATH%
Then type 'bash', and in the bash session, try your curl command again. This should work.