Are you using Visual Studio? I’m not certain what exactly you need to check but here’s a list of things to do:
Check CustomBuildRules and ensure that the 4.0 rule is selected instead of the 3.2 one
Check build properties and look at the build commandline
The commandline found in 2 will show you where the nvcc being used is. Run the nvcc at that address with the argument --version to confirm the nvcc is 4.0