By mistake bought tickets to Huyi station wanting to go to Xi'an

Huyi is too far from Xian city area, by bus it is very hard. The best way is to pay a price difference on the train and continue your trip to Xian North. After your boarding, you can find a staff and inform them that you want to continue the trip to Xian North instead of getting off at Huyi. You can pay a difference in cash. The only problem is that you may not have a seat for the Huyi-Xian section is all seats are full. You need to stand during this section.