The Little Gem Magnolia growing zones are 7 - 9. You live in 6b, according to the zone lookup on NGA. That means, unless you live in a micro-climate within Stockton, the tree will be marginal - it could do well until you have a cold winter and then it will die. Sorry!
It would be safer to plant a tree hardy in your area then to plant a tree that is marginal for your area. I can think of two small growing Magnolias that will do well: Star magnolia (Magnolia stellata) - my personal favorite, and Sweetbay magnolia (Magnolia virginiana).
To plant a tree, dig a hole twice the size of the pot (deep and wide). Do you know what kind of soil you have in your area? Does it drain well? We do not recomment supplimenting the soil with anything unless the native soil is truly terrible. Make sure to plant your new tree just a little higher than it was in the nursery pot (because the soil will sink) and water it well. Keep it damp but not soggy.
Good luck! Keep us posted.