[Tex/LaTex] Changing fontsize for fancyhdr

fancyhdrfontsize

When changing the article font size to 12pt it changed the font size for all text including fancyhdr. I want to change the header to be around 9pt or 10pt so there are no overlapping words in my document. 

\documentclass[12pt]{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsthm}
\usepackage{amsfonts}
\usepackage{graphicx}
\usepackage{tikz}
\usepackage{fancyhdr}
\usepackage{extramarks}
\usepackage{enumitem}
\usepackage{mathrsfs}


\topmargin=-0.45in
\evensidemargin=0in
\oddsidemargin=0in
\textwidth=6.5in
\textheight=9.0in
\headsep=0.25in

\linespread{1.1}



\pagestyle{fancy}
\lhead{Name}
\chead{Math 310 Introduction to Mathematical Proofs\ (Professor Homework 4)}
\rhead{August 3}
\cfoot{\thepage}


\renewcommand\headrulewidth{0.4pt}
\renewcommand\footrulewidth{0.4pt}
\def\mathLarge#1{\mbox{\LARGE $#1$}}
\renewcommand{\qedsymbol}{$\blacksquare$}

\setlength\parindent{0pt}

\newcommand{\enterProblemHeader}[1]{
\nobreak\extramarks{}{Problem \arabic{#1} continued on next page\ldots}\nobreak{}
\nobreak\extramarks{Problem \arabic{#1} (continued)}{Problem \arabic{#1} continued on next page\ldots}\nobreak{}
}

\newcommand{\exitProblemHeader}[1]{
\nobreak\extramarks{Problem \arabic{#1} (continued)}{Problem \arabic{#1} continued on next page\ldots}\nobreak{}
\stepcounter{#1}
\nobreak\extramarks{Problem \arabic{#1}}{}\nobreak{}
}

\setcounter{secnumdepth}{0}
\newcounter{partCounter}
\newcounter{homeworkProblemCounter}
\setcounter{homeworkProblemCounter}{1}
\nobreak\extramarks{Problem \arabic{homeworkProblemCounter}}{}\nobreak{}

\newenvironment{homeworkProblem}[1][-1]{
\ifnum#1>0
    \setcounter{homeworkProblemCounter}{#1}
\fi
\section{Problem \arabic{homeworkProblemCounter}}
\setcounter{partCounter}{1}
\enterProblemHeader{homeworkProblemCounter}
}{
\exitProblemHeader{homeworkProblemCounter}
}

\begin{document}

\end{document}

Best Answer

Quick hack:

\pagestyle{fancy}
\lhead{\fontsize{9pt}{11pt}\selectfont Name}
\chead{\fontsize{9pt}{11pt}\selectfont Math 310 Introduction to Mathematical Proofs\ (Professor Homework 4)}
\rhead{\fontsize{9pt}{11pt}\selectfont August 3}
\cfoot{\thepage}
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