You have to write hard enough to make sure it goes through to the carbon copy.
You have to press down hard enough with your pen to make sure it transfers through.
1) You have to write hard enough to make sure it goes through to the carbon copy.
「複写になっているのでしっかり写るように強く書いてください。」
「複写」のことを carbon copy と言います。
make sure it goes through で「しっかり写るように」
2) You have to press down hard enough with your pen to make sure it transfers through.
「しっかり転写するように強い筆圧で書いてください。」
make sure it transfers through で「しっかり転写するように」
ご参考になれば幸いです!