What is called a promise in Buddhism?

I'm a 16 year old girl and at a time in my life,I have been used to watch inappropriate things. When my parents found this out,my mom got me promised to her in front of Buddha to not to do it, and I promised her with pure intention of keeping it. Then by the time, when I just turned out to be a teenager I just got and urge and curiosity to see them and I watched them again. Is this even a promise, if it is a promise according to Buddhism then have I done a sin?