How do I resize an image without stretching out/distorting in C#?

using System;
using System.Drawing;
using System.Windows.Forms;

namespace ThumbnailImg
{
    public partial class Form1 : Form
    {
        Image imgThumb;

        public Form1()
        {
            InitializeComponent();
        }

        public Image ImgThumb { get => imgThumb; set => imgThumb = value; }

        private void btnOpen_Click(object sender, EventArgs e)
        {
            if (openFileDialog1.ShowDialog() == System.Windows.Forms.DialogResult.OK)
            {
                txtFileNm.Text = openFileDialog1.FileName;
                MessageBox.Show("Image Uploaded");
            }
        }

        private void btnSave_Click(object sender, EventArgs e)
        {
            

            try
            {
                Image image = null;
                // Check if textbox has a value
                if (txtFileNm.Text != String.Empty)
                    image = Image.FromFile(txtFileNm.Text);
                // Check if image exists
                if (image != null)
                {
                    ImgThumb = image.GetThumbnailImage(100, 100, null, new IntPtr());
                    this.Refresh();
                    ImgThumb.Save("C:\\Users\\Acer\\Pictures\\Camera Roll\\thumbnail.jpg");
                    MessageBox.Show("Image saved successfully");
                }
            }
            catch
            {
                MessageBox.Show("An error occured");
            }
        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            if (ImgThumb != null)
                e.Graphics.DrawImage(ImgThumb, 30, 20, ImgThumb.Width, ImgThumb.Height);
        }
    }
}