Surah Taha (20:85-87 and 20:95-97) states that the calf worshipped by the Israelites was made by a Samaritan but neither the country of Samaria (where Samaritans come from) nor the term Samaritan existed during this time (the time of the Exodus) and so it is certain that Moses (sws) could not have used the term or had any dealings with a Samaritan. The term was not used by anyone until around 722 BC, hundreds of years after Exodus. Thus, the Qur'anic claim of being error free cannot be justified.
The Holy Qur'an has not indicated the fact that the man who made the calf was a Samaritan. It only mentions the name 'Assamiri. It is only one of the interpretations of the word that led you to form such an opinion about the divine book. The question as to who was this 'Assamiri' has been subject of different interpretations. Some of the interpreters hold that the name shows that it is an attribution to a certain tribe. There are counter interpretations and the one offered by Abdul Majid Darya Abadi, based on the Jewish sources is worth mentioning. He writes:
The word sounds more of an appellation than of a personal name. If we look to old Egyptian, we have Shemer, a stranger, and foreigner. As the Israelites had just left Egypt, they might quite well have among them an Egyptian Hebrew bearing that nickname. And it is recorded by the rabbis that the initiative in the matter of the calf worship was taken not by the Israelites but the Egyptians who had joined them at the time of the Exodus, and who were the source of a great deal of trouble to Moses and Israelites. (JE. III, P. 509).1
This, I think, is the most acceptable interpretation of all. If somebody claims that the word 'Assamiri' refers to a particular tribe, a country or a culture of a specific period he must substantiate his claim first to merit consideration.
1. Tafsiru'l-Qur'an, 'Abdu'l-Majid Daryabadi, 1st ed., vol. III, (Karachi: Daru'l-Isha'at, 1991), p.113-4