How to make soft/rounded edges using PathGeometry in .xaml C#

I am trying to draw in C# for the first time and I have a problem with positioning. I made some background but I have problem to finish it. I always destroy the whole figure...

I need to change down edges and make them soft/rounded like on mobile screen. I have tried to change this, but I don't understand where to input <ArcSegment>(or some other command) and how to rotate that part of edge.

This is how my .xaml code looks:

<Path.Data>
     <PathGeometry>
          <PathFigure StartPoint="0,0">
              <ArcSegment Size="50,50" RotationAngle="180" IsLargeArc="True" SweepDirection="Clockwise" Point="500,0"/>
                    <LineSegment Point="500,400"/>
                    <LineSegment Point="450,500"/>
                    <LineSegment Point="50,500" />
                    <LineSegment Point="0,400"/>
                    <LineSegment Point="0,0" />

          </PathFigure>
     </PathGeometry>
</Path.Data>

After my code I got:

Thank you in advance!

Solution

Here is how I solved my problem.

<LineSegment Point="0,475"/>
<BezierSegment Point1="0,475" Point2="0,500" Point3="25,500" />
<LineSegment Point="475,500" />
<BezierSegment Point1="475,500" Point2="500,500" Point3="500,475" />
<LineSegment Point="500,0" />

I have applied BezierSegment to make rounded/soft edges.

Explanation:
In BezierSegment I have three points. I drew first LineSegment which is going to the first red arrow, then I set the same spot to be the first point. After that I move to spot where is going to be rounded shape, and then I place Point3 which will connect another two. I did the same thing for right part.

Also, you can check curved angle in this answer. There are a lot more things described there. It seems to be the same thing, but I didn't understand how to apply it at that time because I didn't know about the name of BezierSegment and I was confused with all other commands.

At least I presented a specific case of layout and code, hope it will help someone.