5 panel or 10 panel just means how many different drugs they test for.Dilluting isn't a factor except if you over dillute you'll fail for any of the tests.
Yes they do test for specific gravity.That along creatine levels,specific gravity and color is how they test for dillution.

I still think you're probably in good shape as you haven't smoked much. Just follow the dillution sticky the morning of the test and you'll probably be fine. There is no way for anyone to tell you that you are going to pass 100%.
If you are really concerned the best thing you could do is pickup some synthetic urine.