List off the biggest mistakes new ball python owners make?

[Bogertophis]

I don't know my BP exact age, all of know is that she's young (less than a year old)
Is a scale necessary to monitor her growth/weight?
I've just been watching how sloped her spine is; if that makes sense.
Should I order one as soon as possible?

If you have spare money lying around & don't need to save it for essentials, a digital scale may help put your mind at ease, especially since you seem to be worried. It can also help to weigh the prey if you're not sure what size is appropriate for your snake.

But it's not absolutely necessary. I have a scale & rarely ever use it. I don't routinely weigh any of my snakes & never have- I've been keeping many snakes for decades. My scale is only in case of illness, to calculate a dose of medication- that sort of thing. I use it most often to calculate postage on things I'm mailing...

Also, if you post pics here we can help you assess your snake's weight. One downside of using a scale to keep weighing your snake, especially a new snake, is that the process is rather stressful for the snake, & tends to add to your worries. I can't tell you how many people think their snake is (gasp!) "losing weight" when actually all they did was just take a dump. A snake's weight doesn't have to perfectly conform to a chart- the main thing is that they look & act healthy. It's mostly common sense. Now, if your snake goes on an extended fast, that would be a good time to keep track of their weight. Otherwise, relax... Not all snakes grow at the same rate, any more than humans do. A snake that is slightly underfed is better off (healthier) than one which is over-fed.