I had the same problem with that center piece. You need to follow the directions exactly & don’t overthink it.
I don’t have the pattern right in front of me but once you cut the first grp of triangles, you turn the next one upside down right up against the previous one with no space between then. I actually draw a line around that combined pc. Before I cut it. I have cut paper templates to use to be sure I have them right.
I hope I haven’t mislead you in any way. I’ve now made sev. of them.