Argthtjtr

How could I fix it?

Here is the code:

documentclass[a4paper]{article}

usepackage[utf8]{inputenc}

usepackage[top=1cm,left=1.5cm,bottom=2cm,right=1.5cm,headsep=0.3cm]{geometry} 

usepackage{tikz}

usepackage{graphicx}

usepackage{multicol} 

usepackage{amsfonts,amssymb,amsmath}

usepackage{xcolor}

usepackage{fancyhdr} 

pagestyle{fancy} 

usepackage{pbox}

usepackage{lipsum}



renewcommand{headrulewidth}{1.2pt}% linha no header 

renewcommand{footrulewidth}{1.2pt} % linha no footer



 lfoot{tt Prof. Lucas}

 cfoot{LaTeX}

 rfoot{tt today}





fancypagestyle{firststyle}

{

lhead{

defsc{0.6}

defrc{sc*0.1cm} % rc = 10% de sc

begin{tikzpicture}[scale=sc]

definecolor{tempcolor}{RGB}{50,160,65}

filldraw[tempcolor][rounded corners=rc] (0cm,0cm) rectangle (1.2cm,1cm);

end{tikzpicture}

}   

rhead{tikz node at (0,0) { textbf{2ª Prova de Física - 2º Semestre}};\ 

tikz[baseline]{node[anchor=base, draw=black, thick, minimum width=8.5cm, minimum height=7mm,rounded corners, yshift=-2mm,label={[fill=white,label distance=-2mm,inner xsep=2pt]90:{tt Aluno(a)}:}] { phantom{tt 15,0} };}   

tikz[baseline]{node[anchor=base, draw=black, thick, minimum width=2cm, minimum height=7mm,rounded corners, yshift=-2mm,label={[fill=white,label distance=-2mm,inner xsep=2pt]90:{tt Turma}:}] {phantom{tt 15,0}};}   

tikz[baseline]{node[anchor=base, draw=black, thick, minimum width=1.5cm, minimum height=7mm,rounded corners, yshift=-2mm,label={[fill=white,label distance=-2mm,inner xsep=2pt]90:{tt Valor}:}] { tt 15,0};} 

tikz[baseline]{node[anchor=base, draw=black, thick, minimum width=1.5cm, minimum height=7mm,rounded corners, yshift=-2mm,label={[fill=white,label distance=-2mm,inner xsep=2pt]90:{tt Nota}:}] {phantom{tt 15,0}};}

}

 lfoot{tt Prof. Lucas}

 cfoot{LaTeX}

 rfoot{tt today}

}



setlength{headsep}{dimexprheadsep+1.2baselineskip+.4pt}



begin{document}



thispagestyle{firststyle}



begin{multicols}{2} 



lipsum[3-20]



end{multicols}



end{document}

Your document produces the warning

Package Fancyhdr Warning: headheight is too small (12.0pt): 

 Make it at least 44.28043pt.

 We now make it that large for the rest of the document.

 This may cause the page layout to be inconsistent, however.

so adding

setlengthheadheight{45pt}

to the preamble would make things look better.

use

 usepackage[top=5mm,includehead,headheight=45pt,

             left=1.5cm,bottom=2cm,right=1.5cm,headsep=0.3cm]{geometry}