Pagerank has nothing to do with the sandbox. For most gambling keywords, Google will place your site in the sandbox for 12-24 months. Our site is starting to come out of the sandbox the past couple of months after 18 months in the sandbox, but it is a gradual process.
To your original question of how you know if you are in the sandbox.
1) Do a search for your site in Google using the keywords you are optimizing for
2) Do another search in Google, this time add “allinanchor:” just before the keywords you are optimizing for
3) Compare the results
You are in the sandbox if the results for these 2 searches are quite different. If the results are close together, say within 10-20 results then you are not in the sandbox.
One note to all of this, gambling keywords are probably the most competitive in the world, so even if you aren’t in the sandbox you may not be ranking anywhere near the top of the results. It will take most webmasters at least a year to get anywhere near the top anyway, so in a way the sandbox is almost a moot point since it takes forever to rank anyway.