Forecasting issue

Dear Forum Members,

I have a problem with forecasting. Attached is the file in which I forecasted sales for 2018. On the left side is an example I used from the internet. On the right side is the same method applied to my own data. Or at least I did best to duplicate the method. I did manage to duplicate everything, however the forecasted sales seem way off. My question to you is if you could be so kind to take a look at the Excel sheet attached.

Thank you in advance, hope to hear from you soon.

Cordially,

Bremmes