AES key converting to string and byte[] C#

I have an application that generates a AES Key (using Security.Cryptography). I take that AES Key, convert it to string and put it in a cookie like this:

string keyToSend = Encoding.UTF8.GetString(CurrentKey);
HttpCookie sessionKeyCookie = new HttpCookie("SessionKey", JsonConvert.SerializeObject(keyToSend));

keyToSend looks like this: "���K��Ui ����&��Ӂ*��()".

Then, I want to take back that key and use it to decrypt something, and I do this:

string keyString = JsonConvert.DeserializeObject<string>(context.Cookies["SessionKey"].Value);
byte[] ascii = Encoding.ASCII.GetBytes(cevaString);
byte[] utf8 = Encoding.UTF8.GetBytes(cevaString);
byte[] utf32 = Encoding.UTF32.GetBytes(cevaString);

Also, my keyToString looks like this: "���K��Ui ����&��Ӂ*��()".

And my browser cookie looks like this: "�\u0010��K��Ui �\u0010�\u000f�\u001f\u0005�\u0012\u0018&��Ӂ*��()\u001e"

The initial key should have 256bits, so 32 entries in that array, but all my variables (ascii, utf8, utf32) have different lengths. Why is that, how can I retrieve the cookie and convert it to a byte[32] array?