placing the full width table caption on top of the table in tufte-latex book

Question

I am using tufte-latex book format for writing my thesis. I have a full width table which I can easily define within table* environment in tufte book. As far as I understood, the caption should also be full width. However, I still get it on the right margin. Any idea how to solve this issue? I also want the caption to be placed on the top of the table. Here is my MWE:

\documentclass[nols,a4paper,justified,marginals=auto]{tufte-book}
\usepackage{makecell}
\usepackage{booktabs}
\usepackage{multirow}
\renewcommand{\arraystretch}{1.2}
\usepackage[flushleft]{threeparttable}
\begin{document}
  \begin{table*}[h!]
  \centering
  \begin{threeparttable}
    \caption{here I have a long caption that I want it to be in the fullwidth format as the table but I get it in margin.\label{table3}}%
    \begin{tabular}{llllllllllllllllllll}%
      A&B&C&D&E&F&G&H&I&J&K&L&M&N&O&P\\%
     0.50&$0.47^{a}$&0.48&0.50&0.47&0.48&0.60&0.39&1.00&\0.48&0.50&0.47&0.48&0.60&0.39&1.00\%
    \end{tabular}%
    \begin{tablenotes}
       %\footnotesize
       \item $^{a}$ some extra information about this number.
    \end{tablenotes}
  \end{threeparttable}
\end{table*}
\end{document}

Thanks in advance.