Like this:
\documentclass{article}
\usepackage{karnaugh-map}
\usepackage[margin=1cm]{geometry}
\begin{document}
\begin{karnaugh-map}[4][2][1][$C$][$B$][$A$]
\minterms{3,2,5,7}
\autoterms[0]
\implicant{3}{2}
\implicant{5}{7}
\end{karnaugh-map}\hfill \hspace{-.5cm}%
\begin{karnaugh-map}[4][2][1][$C$][$B$][$A$]
\minterms{3,2,5,7}
\autoterms[0]
\implicant{3}{2}
\implicant{5}{7}
\implicant{3}{7}
\end{karnaugh-map}\hfill \hspace{-.5cm}%
\begin{karnaugh-map}[4][2][1][$C$][$B$][$A$]
\minterms{3,2,5,7}
\autoterms[0]
\implicant{0}{1}
\implicantedge{4}{4}{6}{6}
\end{karnaugh-map}
\end{document}
Output:

I make the text width greater with geometry package.
Before I tried to make smaller characters without success (perhaps You need to change the package karnaugh-map).
EDIT If You want 4 maps on two lines, You dont need minipage or geometry package:
\documentclass{article}
\usepackage{karnaugh-map}
%\usepackage[margin=1cm]{geometry}
\begin{document}
\begin{karnaugh-map}[4][2][1][$C$][$B$][$A$]
\minterms{3,2,5,7}
\autoterms[0]
\implicant{3}{2}
\implicant{5}{7}
\end{karnaugh-map}\hfill \hspace{-.5cm}%
\begin{karnaugh-map}[4][2][1][$C$][$B$][$A$]
\minterms{3,2,5,7}
\autoterms[0]
\implicant{3}{2}
\implicant{5}{7}
\implicant{3}{7}
\end{karnaugh-map}\hfill \hspace{-.5cm}%
\indent
\begin{karnaugh-map}[4][2][1][$C$][$B$][$A$]
\minterms{3,2,5,7}
\autoterms[0]
\implicant{0}{1}
\implicantedge{4}{4}{6}{6}
\end{karnaugh-map}\hfill \hspace{-.5cm}%
\begin{karnaugh-map}[4][2][1][$C$][$B$][$A$]
\minterms{3,2,5,7}
\autoterms[0]
\implicant{0}{1}
\implicantedge{4}{4}{6}{6}
\end{karnaugh-map}
\end{document}
Output:

LAST EDIT You van put also more than 3 k-maps on the same line, without geometry or minipage, with resizebox:
\documentclass{article}
\usepackage{karnaugh-map}
\begin{document}
\resizebox{.95\columnwidth}{!}{%
\begin{karnaugh-map}[4][2][1][$C$][$B$][$A$]
\minterms{3,2,5,7}
\autoterms[0]
\implicant{3}{2}
\implicant{5}{7}
\end{karnaugh-map}\hfill \hspace{-.5cm}%
\begin{karnaugh-map}[4][2][1][$C$][$B$][$A$]
\minterms{3,2,5,7}
\autoterms[0]
\implicant{3}{2}
\implicant{5}{7}
\implicant{3}{7}
\end{karnaugh-map}\hfill \hspace{-.5cm}%
\begin{karnaugh-map}[4][2][1][$C$][$B$][$A$]
\minterms{3,2,5,7}
\autoterms[0]
\implicant{0}{1}
\implicantedge{4}{4}{6}{6}
\end{karnaugh-map}
}
\end{document}
Output:
