What is the halacha if one made a promise and afterwards realized that it is inappropriate?

Many years ago  I was sitting around my family and my mother complained that she doesn’t own a car. I told her that I will buy her one to cheer her up! (I may have thought at the time that I would get this done). Now that I am older, I realize that this is far beyond my budget and I wish I never said those words. Ever since then, these words are in the back of my mind. Is this a real neder (vow)? I may not have thought this clearly when I said it especially since my mother was sad.

Thank You