Uploading image as thumbnail asp .net core web api

Question

I'm made a post api that takes an image and upload it as original version in a folder called images, and as a thumbnail image in folder called thumbnail, I'm working with Bitmap to resize the image resolution, but when I tried my api, the two versions of the same uploaded image were the same size, so it seems Bitmap isn't resizing my image, here is my code:

 [HttpPost, DisableRequestSizeLimit]
        [Route("add-image/{id}")]
        public async Task<IActionResult> uploadImage([FromRoute]long id)
        {
            try
            {
                var formCollection = await Request.ReadFormAsync();
                var file = formCollection.Files.First();

                var folderName = Path.Combine("Resources", "Images");
                var pathToSave = Path.Combine(Directory.GetCurrentDirectory(), folderName);

                if (file.Length > 0)
                {
                    var fileName = DateTime.Now.Second.ToString().Trim(' ', '/')+ContentDispositionHeaderValue.Parse(file.ContentDisposition).FileName.Trim('"');
                    var fullPath = Path.Combine(pathToSave, fileName);
                    var dbPath = Path.Combine(folderName, fileName);

                    using (var stream = new FileStream(fullPath, FileMode.Create))
                    {
                        file.CopyTo(stream);
                    }

                    var ThumbFolder = Path.Combine("Resources", "Thumbnails");
                    var pathToSaveThumb = Path.Combine(Directory.GetCurrentDirectory(), ThumbFolder);
                    var ThumbFilName = $"thumb{fileName}";
                    var fullPathThumb = Path.Combine(pathToSaveThumb, ThumbFilName);
                    var DbThumbpath = Path.Combine(ThumbFolder, ThumbFilName);


                    Image img = Image.FromFile(fullPath);

                        var newWidth = img.Width / 10;
                        var newHeight = img.Height / 10;
 
                        Bitmap bmp = new Bitmap(img);
                        var graphic = Graphics.FromImage(bmp);
                        graphic.InterpolationMode = InterpolationMode.HighQualityBicubic;
                        graphic.SmoothingMode = SmoothingMode.HighQuality;
                        graphic.PixelOffsetMode = PixelOffsetMode.HighQuality;
                        graphic.CompositingQuality = CompositingQuality.HighQuality;
                        graphic.DrawImage(img, 0, 0, 100, 50);
                        bmp.Save(fullPathThumb);

                        var imageToSave = bmp;
   

                    ClientImage dbImage = new ClientImage()
                    {
                        ClientId = id,
                        ImageUrl = dbPath
                        
                    };

                    await _trainingContext.AddAsync(dbImage);
                    await _trainingContext.SaveChangesAsync();


                    return Ok(dbImage.ImageUrl);
                }
                else
                {
                    return BadRequest();
                }
            }
            catch (Exception e)
            {

                return StatusCode(500, $"Internal Server Error {e.Message}");
            }
        }

What am I doing wrong?

any answer will be very appreciated, Thank you!