'10 Prius won't shift out of park, yellow triangle warning

I just got done replacing the spark plugs using the tutorial video here. The engine starts up just fine but when I try to shift out of park I can hear a small click underneath the car and I get a yellow triangle warning, the dashboard tells me to shift it back into park. Any ideas?

 

Turns out me being an idiot was the problem. The door was opened and I automatically assumed the car wasn't shifting. Thanks though!