Hi & welcome @jan
No question is a rookie question and the reply will help you and many others in the future 
So thank you for asking
When selecting a point in the middle of a curve, you need to select the curve, the point and then the curve again, otherwise you will get the curve up to the point and then a straight line after it to the next point.
Since you have already created your detail, you can use the Insert Node tool under the Details tab on the left:
Here is a previous topic on using the Insert Node tool: Make changes to a pattern piece after it's made - #2 by slspencer
If you need any further help, please feel free to ask