I can't open the file. I'm guessing you have RR Track version 5. I have version 4 which isn't compatible. If you could post up a jpeg that would help.
In order to connect to the O72 Y you have to use the 1 3/8 fitters. Your track software should show a 1.375" makeup straight listed with the O72 Y and O72 and O60 switches. These pieces have part of the roadbed removed so they can fit into the center of the Y, otherwise the roadbed from joining pieces would hit each other.