# Placing equation numbers on the right

I am new to TeX and am using scribtex to write a maths paper. When I put the followng code, the equation number is automatically displayed on the left, instead of in the right as is usually done. What is the problem and how do I fix it? Thanks for your time.

\documentclass[12pt,oneside]{amsart}
\usepackage{amssymb}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\begin{document}
Let us consider a spherical symmetric metric in curvature coordinates:
$$\label{metric} ds^2=-e^\lambda dr^2-r^2(d\theta^2+\sin^2\theta d\phi^2)+e^\nu dt^2$$
\end{document}​

The output I get is:

-