New Post: DataChunk header in wrong position

I am quite new at using naudio and I am following an example provided I found on this site to trim wav files. I am using the example along with my own code to determine the lengths of wave files and trimming them to be at a length that I can use.

The program works great, it trims them perfectly everytime, exactly how I need them except for the datachunk. It is always 2 positions forward. Looking at my wav file in HxD, my original wav file datachunk is in position 37-40.

After I trim the file the datachunk is in position 39-42. This causes a problem in the other program I an using to look at the files. I have tried opening in Audacity and exporting and the datachunk position gets corrected, not sure why but it does. I have also altered the position in HxD and that works too but I would rather not have to go through all of the extra steps if I do not have to.
As I am new to naudio I am unsure if I am doing something wrong (Very possible) and I have looked for similar problems for a few days now and cannot find a single solution.

Here is the code I found through this site. The rest of my code just determines the amount that I need to trim based on the lot of files I am altering. I just read a wave file, trim and store in a different folder.

any help would be greatly appreciated, if you need any more information please let me know and I will provide what I am able to.

 public static void TrimWavFile(string inPath, string outPath, TimeSpan cutFromStart, TimeSpan cutFromEnd)
        {
            using (WaveFileReader reader = new WaveFileReader(inPath))
            {
                using (WaveFileWriter writer = new WaveFileWriter(outPath, reader.WaveFormat))
                {
                    int bytesPerMillisecond = reader.WaveFormat.AverageBytesPerSecond / 1000;

                    int startPos = (int)cutFromStart.TotalMilliseconds * bytesPerMillisecond;
                    startPos = startPos - startPos % reader.WaveFormat.BlockAlign;

                    int endBytes = (int)cutFromEnd.TotalMilliseconds * bytesPerMillisecond;
                    endBytes = endBytes - endBytes % reader.WaveFormat.BlockAlign;
                    int endPos = (int)reader.Length - endBytes;

                    TrimWavFile(reader, writer, startPos, endPos);
                }
            }
        }

        private static void TrimWavFile(WaveFileReader reader, WaveFileWriter writer, int startPos, int endPos)
        {
            reader.Position = startPos;
            byte[] buffer = new byte[1024];
            while (reader.Position < endPos)
            {
                int bytesRequired = (int)(endPos - reader.Position);
                if (bytesRequired > 0)
                {
                    int bytesToRead = Math.Min(bytesRequired, buffer.Length);
                    int bytesRead = reader.Read(buffer, 0, bytesToRead);
                    if (bytesRead > 0)
                    {
                        writer.WriteData(buffer, 0, bytesRead);
                    }
                }
            }
        }