Formatting table in latex - latex

Question

I would like to ask how to format table above in latex - table is pretty decent but I would like to have "model" bit right not at the very end, also I would like to have no space at the very right of the table.
\documentclass{article}
\usepackage[utf8]{inputenc}
\title{table in stack}
\author{petr102030 Hrobar}
\date{November 2019}
\begin{document}
\maketitle
\section{Introduction}
\begin{table}[!htbp] \centering
\label{exp_rmse}
\begin{tabular}{#{\extracolsep{5pt}}lccccccc}
\\[-1.8ex]\hline
\hline \\[-1.8ex]
Model & \multicolumn{1}{c}{RMSE} & \multicolumn{1}{c}{MAE} & \multicolumn{1}{c}{MAPE} & \\
\hline \\[-1.8ex]
Holt-Winters (add.) & 1256.361 & 924.962 & 3.518 &\\
Holt-Winters (mul.) & 1238.799 & 909.395 & 3.457 &\\
Parab. Trend (model 4) & 2228.310 & 1792.471 & 7.959 &\\
Lin.Trend (model 5) & 3074.307 & 2545.426 & 11.339 &\\
\hline \\[-1.8ex]
\end{tabular}
\end{table}
\end{document}

Answer 1

The "Model" is at the leftmost boarder of your table because the default padding is shallowed by #{\extracolsep{5pt}}. If you remove this, you'll get the padding back. (However the usual advice is to remove this padding, so please consider carefully if you really want to do this)
only specify as many columns as you have in your table and not 8 like in your example
with the siunitx package you can align the numbers nicely by their decimal markers
as already mentioned by Picaud Vincent the booktabs package is very useful to create nice looking tables. Amongst other things, it improves the vertical spacing around rules
using \label{} only makes sense if there also is a caption it can reference
I suggest to remove all the unnecessary \multicolumn{1}{...}, they don't do anything useful and can mess up the formatting
\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{booktabs}
\usepackage{siunitx}
\title{table in stack}
\author{petr102030 Hrobar}
\date{November 2019}
\begin{document}
\maketitle
\section{Introduction}
\begin{table}[!htbp]
\centering
\begin{tabular}{#{}lS[table-format=4.3]S[table-format=4.3]S[table-format=2.3]}
\toprule
Model & {RMSE} & {MAE} & {MAPE} \\
\midrule
Holt-Winters (add.) & 1256.361 & 924.962 & 3.518 \\
Holt-Winters (mul.) & 1238.799 & 909.395 & 3.457 \\
Parab. Trend (model 4) & 2228.310 & 1792.471 & 7.959 \\
Lin.Trend (model 5) & 3074.307 & 2545.426 & 11.339 \\
\bottomrule
\end{tabular}
\end{table}
\end{document}