Apply specific format to word in rmarkdown

Question

I am using rmarkdown and I want the Country "Afghanistan" to become HUGE, Center and in Oswald Regular I tried \Centering\Huge but I failed.

---
documentclass: report
classoption: twoside
fontsize: 12pt
output: 
  pdf_document: 
    latex_engine: xelatex
    keep_tex: true
keep_tex: true
header-includes: |
  \usepackage{geometry}
  \geometry{a4paper,asymmetric,
  top=3.5cm,left=2cm,right=2cm,bottom=1cm,
  headsep=0pt,footskip=0pt,
  headheight=200pt}
  \usepackage{fontspec}
  \setmainfont{Roboto-Regular}[Extension = .ttf,BoldFont = Roboto-Bold,ItalicFont = Roboto-LightItalic,BoldItalicFont = Roboto-BoldItalic]
  \newfontfamily\oswaldfont{Oswald Regular}

---
\noindent 
\oswaldfont{Afghanistan} \newline

\bigskip
 
\begin{minipage}[t]{0.4\linewidth}
  minipage1
\end{minipage}
\hfill
\begin{minipage}[t]{0.4\linewidth}
  minipage2
\end{minipage}

The gambia