I made a vow, but I am not sure if I had reached puberty. What should I do?

The vow of a child is not binding because the pen has been lifted from him. If you were a pubescent at the time of the vow, then you are obliged to fulfill it. If you are certain or fairly certain that you were not yet pubescent, then there is nothing upon you. However, if you are unsure whether you reached puberty, the default is the exoneration of responsibility, so you are not obliged to fulfill the vow, because relying on the original state – which is not having reached puberty – is sufficient to lift the burden.