All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.
According to our knowledge, nothing was reported on the authority of the Prophet that indicates that sins are forgiven on the day of 'eid. The Muslim is enjoined to sincerely repent for all his sins and should know that as long as he sincerely repents to Allaah, then all his sins, as grave as they may be, will be forgiven. The Prophet said, "The one who repents from sin is like the sinless person." [Ibn Maajah]
Allaah knows best.