Reference: Fataawa al-Hajj wal-‘Umrah waz-Ziyaarah – Page 59
Question: A year ago, I performed the ‘umrah and was ignorant of some of the conditions. When I entered the state of ihraam at the meeqaat, I wore a pair of shorts and I was ignorant about this issue. When I returned, some people informed me that this is not permissible so I performed the ‘umrah [again] this year according to that which I learnt, that it is not permissible to wear any stitched garment. Therefore, is there anything required of me in that case?
Response: There is no expiation for you to make, since you were ignorant of the ruling. So, ignorance is an excuse in this impermissible act, whilst the expiation is required from one who knows of the ruling and did so intentionally. So you are not required to repeat the ‘hmrah since you have not done anything to spoil it and the second ‘umrah is considered as a voluntary one.