Custom Shape for Container - flutter

Question

Idea is to make a custom shaped container by giving it ShapeDecoration().
I used this thread as a reference.
Eventialy I achieved the shape I wanted, but once I wrap this custom shaped container with margin\padding\SizedBoxes around it - it's content is being pushed out of the bounds of the container. Check out screenshots.
Normaly it should be smth like this:
but with paddings between elements.
So the problem is that my customized container behavers realy wierd once it has any margin\padding arround it.
return Padding(
padding: const EdgeInsets.symmetric(vertical: 40),
child: Container(
padding: const EdgeInsets.all(8),
height: 88,
alignment: Alignment.center,
decoration: ShapeDecoration(
shape: UnitListItemBorderShape(
color: _isCurrent ? theme.listItemBorderColor : theme.listItemBackgroundColor,
),
color: theme.listItemBackgroundColor,
),
child: Stack(
children: [
//custom container's ineer content
] ,
),
);
UnitListItemBorderShape class:
class UnitListItemBorderShape extends ShapeBorder {
const UnitListItemBorderShape({color}) : _color = color;
final Color _color;
#override
EdgeInsetsGeometry get dimensions => const EdgeInsets.all(0);
#override
Path getInnerPath(Rect rect, {TextDirection textDirection}) => null;
#override
Path getOuterPath(Rect rect, {TextDirection textDirection}) => UnitListItemShape.getShape(
rect.width,
rect.height,
const Radius.circular(16),
const Radius.circular(20),
);
#override
void paint(Canvas canvas, Rect rect, {TextDirection textDirection}) {
final Paint borderPaint = Paint()
..color = _color
..style = PaintingStyle.stroke
..strokeWidth = 2;
canvas.drawPath(getOuterPath(rect), borderPaint);
}
#override
ShapeBorder scale(double t) => null;
}
UnitListItemShape class:
class UnitListItemShape {
static Path getShape(double width, double height, Radius borderRadius, Radius circleRadius) {
final double rightOffset = circleRadius.x;
final Rect rect = Rect.fromCenter(center: Offset(width - rightOffset - 4, height / 2), width: 48, height: 48);
return Path()
..moveTo(borderRadius.x, 0)
..lineTo(width - borderRadius.x - rightOffset, 0)
..arcToPoint(Offset(width - rightOffset, borderRadius.x), radius: borderRadius)
..lineTo(width - rightOffset, (height / 2) - rightOffset - 4)
// ..addRect(rect)
..arcTo(rect, -70 * math.pi / 180, 150 * math.pi / 180, false)
..lineTo(width - rightOffset, height - borderRadius.x)
..arcToPoint(Offset(width - borderRadius.x - rightOffset, height), radius: borderRadius)
..lineTo(borderRadius.x, height)
..arcToPoint(Offset(0, height - borderRadius.x), radius: borderRadius)
..lineTo(0, borderRadius.x)
..arcToPoint(Offset(borderRadius.x, 0), radius: borderRadius)
..fillType = PathFillType.evenOdd
..close();
}
}