International travel question (important)?

hey. im traveling to colombia tomorrow. i was born in USA. and i have a american pport. when i was younger i remember my mom typing out a paper and had to go to some place to get a special stamp. my mom doesnt remember if she has to get the paper for me to leave the country and enter colombia or leave colombia and enter USA. im traveling alone and im 15 years old. i need answer asap. please thanks.