Asalamualykum, I don't believe this is the case. I've never read a sin will be multiplied 7 times.
Am using Tapatalk atm, so I can't search the official answer. Use Islam Q & A website to find the answer.
I believe the answer is no, it's not multiplied. What I have read, is when you have a bad intention, and you don't do the evil act, you won't be punished in sha Allah. On the other hand, Allah is so merciful, if you have a good intention, and you don't even do the good deed, you will be rewarded for your intention in sha Allah.