i have one string, and i assign the value like,
string str=\"admin\" + @\"\\\" + \"user\";
The output of the \"str\" value comes as
I'm sure your string is actually fine.
I am guessing you are looking at the value in the debugger and seeing \\. This is because the debugger is escaping a single \ to \\ to make it clear to you that this is a slash and not a control code.
For example, the debugger shows a tab as \t, so in order to show you a slash followed by the letter t it escapes it to \\t.
If you write this string out to console/log/file, you'll see it is as you expect.