I found below music sheet from one website. I doubt if this piece is correct because there are 12 Eighth Notes are used in one measure. I think it is mathematically wrong. Please help.
As noted in other comments and answers, the notes are explicitly marked with a cursive "3" (fingerings use upright numbers, in contrast) as triplets, 3 notes to the usual 2. It is worth noting that particularly in older scores, the cursive "3" may be missing and the triplets may already be implied by the beaming of three notes to one beam. It can also happen that the "3" is present a few times explicitly and then left off.
As David Bowling noted in the comments: these are triplets. See the little "3"s above the notes? That means you need to play three notes in the time normally assigned to two notes of the given type. So these are eighth triples, three of them amount to two normal eighths, twelve of them amount to eight eighths, and everything turns out to be correct.