double to hex to double lose precision, C#

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static string DblToHex(string dbl)
        {
            return string.Join("", BitConverter.ToString(BitConverter.GetBytes(Convert.ToDouble(dbl))).Split('-').Reverse());
        }
        
        public static string HexToDbl(string hex)
        {
            return BitConverter.ToDouble(Enumerable.Range(0, hex.Length)
                     .Where(x => x % 2 == 0)
                     .Select(x => Convert.ToByte(hex.Substring(x, 2), 16))
                     .Reverse().ToArray(), 0).ToString("E17");
        }
        
        public static void Main(string[] args)
        {
            string hex = "FFD1C05B1E2380B6";
            string dbl = "-4,986180087444250E+307";
            Console.WriteLine(HexToDbl(hex));
            Console.WriteLine(DblToHex(HexToDbl(hex)));
            Console.WriteLine(DblToHex(dbl));
            Console.WriteLine(HexToDbl(DblToHex(dbl)));
        }
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,16 sec, absolute running time: 0,11 sec, cpu time: 0,09 sec, average memory usage: 14 Mb, average nr of threads: 3