Pagerank has nothing to do with the sandbox. The sandbox is applied to most new sites, preventing them from ranking for their competitive keywords. No one knows for sure how to get out of the sandbox, but many people know how to improve their rankings — by optimizing on-page content and gaining backlinks.
Since you have a PR1, that means that you don’t have very many quality links pointing to your site, and regardless of if you are in the sandbox or not, you won’t rank well for any competitive gambling related keywords. PR is one of the factors considered in Googles ranking algorithm, but it is debatable if PR itself does anything for you since it is more of a measure of how many other sites are linking to you.