Latex Column Ending Too Soon - Too Much White Space

Question

So I'm trying to make a standard a1 poster using the a0 document class.

This is my code so far:

\documentclass[poster, a1]{a0poster}
%%%Load packages
\usepackage{multicol}           
\usepackage[left=2cm,right=2cm,bottom=0cm,top=0cm]{geometry}
\usepackage{mathpazo}           
\usepackage{color}              

\definecolor{headingcol}{rgb}{1,1,1}        
\definecolor{boxcol}{rgb}{0.408,0.157,0.376}
\fboxsep=1cm                            
\setlength{\columnsep}{2cm}             

\makeatletter                           
\renewcommand\@maketitle{%
\null                                   
{
    \color{headingcol}\sffamily\veryHuge        %Set title font and colour
    \@title \par}%
\vskip 0.6em%
{
    \color{white}\sffamily\large                %Set author font and colour
    \lineskip .5em%
    \begin{tabular}[t]{l}%
        \@author
    \end{tabular}\par}%
\vskip 1cm
\par
}
\makeatother

\title{TEXT HERE}

\author{NAME \\ Supervisor: NAME}

\begin{document}

\hspace{-3cm}                               %Align with edge of page, not margin
\colorbox{boxcol}{                          %Coloured banner across top
    \begin{minipage}{1189mm}                    %Minipage for title contents
        \maketitle
    \end{minipage}}
\vspace{1cm}

\begin{multicols}{4}    
    \section*{Hello}
    jkboub\\kglhvkjb\\liugiub;ub\\lylyvjhb\\ktftuyvuyvyuvluf\\lubaub
    \columnbreak
    \section*{Hello}
    \columnbreak
    hello
    \columnbreak
    hello
\end{multicols}

\end{document}

and yet the outcome is this:

Why is there some text in the second column, which should be continuing in the first?