Try an office supply store for a digital scale- I've had mine for many years- it only weighs up to 5 lbs, & either oz. or grams, battery operated. Weigh a container
by itself, then with the snake in it, & subtract the weight of the container. Bathroom scales for people aren't precise or accurate enough for weighing snakes.

As already mentioned, offering too often adds stress & makes a snake less likely to eat. Wait 7-10 days between tries, & try not to worry...BPs just do this.