Unfortunately there is no easy way. I'm sure that the "triangle" in your street has a lot more sides than a scope pivot technique can handle.
You can try to split that shape down to a three edge triangle or a rectangle or a skilled combination of those and use insertAlongUV with a simple geometric shape(s) (rounded triangles or such).
Also, the CE street creation can sometimes create the roundedness you need. But also to note, I'm not entirely sure how your shapes are being created as I only see 2 street centerlines and one node. How did you create those slip lanes?
Lastly, it can really help to have a few basic geometric shape models in your assets folder that you can drag into the scene for small use cases. You can then write some code that makes use of those shapes (e.g. pedestrian island code).