Need help with Espionage

[pat12]

Hey, I am a new mac user and have a MBP Retina with 128GB hard drive.

I downloaded the program Espionage that will be good to password protect and encrypt folders.

In my case, I want to password protect a folder with 20GB, the problem is that when I try that I get the error message that I no longer have the disk space to be able to encrypt and password protect the folder.

I choose AES-128 Sparseimage and Sparsebundle as an option when I did this.

When I then check the space on the computer, I see that encryption of the folder requires approximately 3 x 20GB which I dont have. My question is how I can get around this problem and it should be like this?