You have most likely chosen to automatically receive a push to your device when signing in.
In order to check the Remember me for 14 days box, you will want to click Cancel in the blue pop-up banner at the bottom of the Duo authentication prompt.
Once this initial push is cancelled, you can then check the remember me box and request another push to continue your login.
Note: Rapid pushes back-to-back may generate an error message and you will want to wait about 30 seconds before attempting another push to your device.
If you want to turn off the automatic push, instructions can be found in the How do I turn off Duo Auto Push? article.