Groups of 3?

Our class just got one student bigger!! We had a new student start today. He is very sweet and the class really enjoyed getting to know him today. Now I have 21 students. During math stations, my students were in perfect double partner groups (with 20 kids). Today one of the groups did a great job including our newbie and it seemed to be fine. However, my stations are usually set up for partner work and not groups of 3.

Have you had this problem? What do you do?