\centerline{} command alternative?

The \centerline command should never be used in a LaTeX document (unless you know precisely what you're doing, and probably only in the preamble for some definition). Use

\begin{figure}[htp]
\centering

<whatever>

\end{figure}

and <whatever> (a graphic, a TikZ picture or anything) will be centered.

You can use adjustbox

\documentclass{scrreprt}
\usepackage[export]{adjustbox}  %%  export option makes adjustbox --
                                %%  -- goodies available inside includegraphics command
\usepackage{graphicx}

\begin{document}
X\hrulefill X
\begin{figure}[htp]
\includegraphics[width=1.1\textwidth,center]{example-image-a}
\end{figure}
\end{document}

This is very useful for figures that are wider than \textwidth. Another useful macro will be adjustbox environment with max width option.

\documentclass{scrreprt}
\usepackage[export]{adjustbox}
\usepackage{graphicx}

\begin{document}
X\hrulefill X

This is resized to \verb|1.1\textwidth|
\begin{figure}[htp]
\begin{adjustbox}{center,max width=1.1\textwidth}
\includegraphics[width=1.2\textwidth,center]{example-image-a}
\end{adjustbox}
\end{figure}
\clearpage
The following is not resized:
\begin{figure}[htp]
\begin{adjustbox}{center,max width=1.1\textwidth}
\includegraphics[width=0.7\textwidth,center]{example-image-b}
\end{adjustbox}
\end{figure}

\end{document}

The advantage of max width is that the content is resized only if it exceeds the max width otherwise not.

With tikzpicture environment

I assume that your tikz picture are saved as separate files. Then using adjustbox and tikzscale packages:

\documentclass{article}

\usepackage{graphicx,tikz,tikzscale}
\usepackage{adjustbox}
\usepackage{filecontents}
\begin{filecontents*}{myfig.tikz}
\begin{tikzpicture}[inner sep=0pt, outer sep=0pt]
    \draw[use as bounding box](-20,-20) rectangle (20,20);
    \node at (0,0) (A) {A};
    \node[above right] (B) at (A.north east) {B};
    \draw (A.south west)--(B.north east);
  \end{tikzpicture}
\end{filecontents*}

\begin{document}
X\hrulefill X

This is resized to \verb|1.1\textwidth|
\begin{figure}[htp]
\begin{adjustbox}{max width=1.1\textwidth,center}
\includegraphics[width=1.2\textwidth]{myfig.tikz}
\end{adjustbox}
\end{figure}
\clearpage
The following is not resized:
\begin{figure}[htp]
\begin{adjustbox}{max width=1.1\textwidth,center}
\includegraphics[width=0.7\textwidth]{myfig.tikz}
\end{adjustbox}
\end{figure}
\end{document}