I've had this problem too.
I have noticed that not all scales read the same
if only they did it would make life so much more easier.
If I was you I would stick to the gym ones even though you do weigh a bit more on them you'll get a more accurate and consistent reading because you'll be going there more often.
Make your weigh in the morning (do one morning session) before you drink or *eat anything and wear the same clothing and you'll get a more consistent reading.
*I like exercising in the morning and can't eat before my exercise because I feel queasy and sick when I exercise with a full stomach. Having an empty stomach you get a more accurate reading of what you weigh.
By the way - good on you for joining a gym