That is on the small side, but not unheard of. What concerns me is that its a bit light for that length. I've got a female the is just a bit smaller than that and she weighs in at around 9 pounds. Might want to look at the diet, hydration and enclosure conditions just to make sure everything is where you want it.
Her pee I all normal and very regular, I only got her three weeks ago and found out she had worm, I did deworm her and now she has already started getting heaver thanks for the tips.
They all grow at different rates and conditions, therefor as long as she looks great and his active and eating, the shells hard
then you have nothing to worry about.