"I am really surprised" is a correct and usable sentence in written English. You can use it when you need to express surprise or disbelief about something. For example: "I am really surprised that you finished that project so quickly!".
"I am really surprised to be honest.
I am really surprised by the public reaction".
She added: "I am really surprised there are no lifeguards.
"I am really surprised that they are making a big issue out of this".
Ludwig does not simply clarify my doubts with English writing, it enlightens my writing with new possibilities
Simone Ivan Conte
Software Engineer at Adobe, UK