There is no license. It's just an app, not an open source project.
Asking people to download and run an untrusted Windows executable is a major barrier to demonstrating your skills. I don't even have a Windows machine to hand to try it out on!
Showing the source code would give people a much better idea of what you can do.
If you're not willing to publish the source code (and that's a perfectly reasonable decision, it's your work!) I suggest creating a video that demonstrates the project.