You said:

Put your hand under the automatic paper towel dispenser BEFORE washing your hands, so you can do it again after and get an adequate amount of towel

into Japanese

あなたの手を洗う前にあなたの手を自動ペーパータオルディスペンサーの下に置いてください。それでもう一度やり直して十分な量のタオルを手に入れることができます

Back into English

Please put your hand under the automatic paper towel dispenser before washing your hands. Then you can try again and have enough towels