join lines

Hey people,

So i am trying to join line segments into one line. In order to create the lines i draw one line in Rhino and mirror it with Grasshopper. Then i make 2 biarcs in between those lines. So i end up with 6 line segments. When i want to join them i get some trouble with one biarc. I know it has to do with the start and end tangent that i give as an input. 

Anybody has an idea how to solve this?