Flutter Sliding Up Panel makes trouble in my code - flutter

Question

I am a junior developer currently under development in Flutter.
I am currently working on a tablet-only UI and hope it will be compatible with the web environment.
So far, there has been no problem, but there has been a problem with the SlidingUpPanel.
Before applying the SlidingUpPanel, the UI is as follows.
I wanted to apply SlidingUpPanel to the red box space at the bottom of this screen.
So I created the code as follows, and the Widget Tree is shown in the following picture.
class HomePage extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
body: SafeArea(
child: Row(
children: [
Expanded(
flex: 1,
child: SlidingUpPanel(
panel: Text('test'),
body: Column(
children: [
SizedBox(
height: 80.0,
child: HomePageAppBar(),
),
Container(
height: 70.0,
color: Color(0xFFF4F4F4),
child: Row(
children: [
SizedBox(
width: 10.0,
),
Text(
'리스트',
style: TextStyle(
fontSize: 20,
fontWeight: FontWeight.w500,
fontStyle: FontStyle.normal,
),
),
],
),
),
Expanded(
flex: 1,
child: DatePickerContainer(),
),
],
),
),
),
SizedBox(
width: 338.0,
child: Container(
color: Color(0XFFF0F0F0),
),
),
],
),
),
);
}
}
However, after applying SlidingUpPanel, the screen changed strangely as follows...
What's the problematic part in my code?
Edit 1
I used Stack Widget and succeeded in getting SlidingUpPanel without breaking the overall UI as follows.
The code is as follows.
Expanded(
flex: 1,
child: Stack(
children: [
DatePickerContainer(),
SizedBox(
width: _getCurrentWindowWidth(context) - 338.0,
child: SlidingUpPanel(
panel: SizedBox(
width: _getCurrentWindowWidth(context) - 338.0,
child: Center(
child: Text('test'),
),
),
),
),
],
),
),
However, when the SlidingUpPanel is dragged up, it appears that the actual width is the same as the width of the entire screen, but only the visible width is cut off as follows: