Combining columns in table doesn't divide my columns equally

Question

I made a table, but when I tried to combine two columns, it didn't divide my table exactly in two, rather one part is larger than the other (as is shown in the image I added). What am I doing wrong? Thanks!

\begin{table}[h!]
  \begin{center}
    \begin{tabular}{|l|c|c|}
    \hhline{|===|}
     \textbf{Trigger} & \multicolumn{2}{c|}{\textbf{99.9\% Efficiency Point [GeV]}}\\
       & |y*| < 0.3 & |y*| < 0.6\\
      \hline
      L1\_J20 & 132 & 141 \\ 
      L1\_J40 & 205 & 215 \\ 
      L1\_J50 & 235 & 247 \\ 
      L1\_J75 & 318 & - \\ 
      L1\_J100 & - & 414  \\ 
      \hhline{|===|}
      \end{tabular}
      \caption{Caption}
      \label{tab:mjj}
  \end{center}
\end{table}

Answer 1

I suggest using the \thead command from makecell to have themulticolumn`argument on two lines.

\documentclass{article}
\usepackage[T1]{fontenc}

\usepackage{makecell, hhline, multirow}
\renewcommand{\theadfont}{\normalsize\bfseries}

\begin{document}

\begin{table}[h!]
  \centering
    \begin{tabular}{|l|c|c|}
    \hhline{|===|}
     \multirowthead{2}{Trigger} & \multicolumn{2}{c|}{\thead{99.9\% Efficiency \\ Point [GeV] }}\\
       & |y*| < 0.3 & |y*| < 0.6\\
      \hline
      L1\_J20 & 132 & 141 \\
      L1\_J40 & 205 & 215 \\
      L1\_J50 & 235 & 247 \\
      L1\_J75 & 318 & -- \\
      L1\_J100 & -- & 414 \\
      \hhline{|===|}
      \end{tabular}
      \caption{Caption}
      \label{tab:mjj}
\end{table}

\end{document}