\documentclass{article}
\usepackage{tikz, pgfplots}
\usepackage{pgfplots}
\begin{document}
% Preamble: \pgfplotsset{width=7cm,compat=1.11}
\begin{tikzpicture}
\begin{axis}
\addplot3[surf,mesh/ordering=y varies]
table {data3.txt};
\end{axis}
\end{tikzpicture}
\end{document}