But this is not actually called sandbox.
The period of which google monitors our site before giving rank is called sandbox . Its actually a testing area
Is your site is new?...
When my sites was new I was on the top for several weeks and then drop far away behind the top 100. Then slowly in months or a year going up (while adding backlinks etc. in the net).
yep, that's what I also observed for couple of my websites. New site is getting rank very soon for couple of keywords and then after sometimes it lost ranking and then again ranking boost up day by day.