While your vehicle is in motion, lift off of the gas pedal and slowly press down on the clutch. Use the shifter to switch into the next gear up. Slowly take your foot off the clutch and push down on the gas.
Just try again. If you accidentally miss one of the required buttons, but still hit C as told, it will just take a picture which is most likely what happened...
While the car is in motion, take your foot off of the gas pedal, press the clutch, and change your gear. Then, gradually take your foot off of the clutch...