I might look inferior to other people now, but I assure you I will have grown more than others by the time I graduate from high school.
ーI might look inferior to other people now, but I assure you I will have grown more than others by the time I graduate from high school.
「私は今は他の人より劣って見えるかもしれませんが、高校を卒業するまでに誰よりも成長してみせます」
to look inferior to other people で「他人より劣って見える」
to assure someone ...で「人に…だと納得させる・確信させる」
to grow で「成長する」
to graduate from high school で「高校を卒業する」
ご参考まで!