Quarter Circle does not fit my initial circle Flutter Painter - flutter

Question

I'm trying to make a loading icon for my loading screen using CustomPaint widget. Unfortunally, it doesn't work as expected...
My quarter circle does not fit in my primary circle, here's a screen of it :
I don't understand why it is doing this...
Here's the code:
import 'package:flutter/material.dart';
import 'package:responsive_sizer/responsive_sizer.dart';
import 'dart:math' as math;
class LoadingPage extends StatelessWidget {
const LoadingPage({Key? key}) : super(key: key);
#override
Widget build(BuildContext context) {
return Column(
children: [
SizedBox(
height: 25.h,
),
Stack(
alignment: Alignment.center,
children: [
Container(
width: 28.w,
height: 28.w,
decoration: BoxDecoration(
color: Colors.transparent,
shape: BoxShape.circle,
border: Border.all(width: 3.w, color: Colors.white.withOpacity(0.2)),
),
),
CustomPaint(
painter: MyPainter(),
size: Size(28.w, 28.w),
),
]
),
SizedBox(
height: 6.h,
),
Text(
"LOADING",
style: Theme.of(context).textTheme.headline2,
)
],
);
}
}
class MyPainter extends CustomPainter {
#override
void paint(Canvas canvas, Size size) {
final Paint paint = Paint()
..strokeWidth = 3.w
..style = PaintingStyle.stroke
..color = Colors.blue;
double degToRad(double deg) => deg * (math.pi / 180.0);
final path = Path()
..arcTo(
Rect.fromCircle(
center: Offset(size.width/2, size.height/2),
radius: 28.w/2,
),
degToRad(90),
degToRad(90),
false);
canvas.drawPath(path, paint);
}
#override
bool shouldRepaint(CustomPainter oldDelegate) => false;
}
Does anyone knows why ? :)
Thanks for your answers,
Chris