I’m scared of weighing myself on the scale.
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means quantity, but you don't "to quantity." To figure out the quantity, however, you have to measure / to weigh whatever it is you want to get the quantity of.
You need to measure the quantity of something, but don't have a scale or anything. Luckily, you are quite the hacker (はか) and hack together a scale using only rubber bands and beans.