I didn't get the 100GB promo space through Acer Jumpstart.

Hi skz, I just sent you an email, in order for us to investigate further.

Please reply back to me, and we'll take it from there. Thanks! 

Yes, I did follow the same steps and because of it, the screen showed me the promotional offer of 100GB storage space.

After then only my account got created, but didn't get that 100GB storage.

The extra 100 GB from the Acer promotion usually requires you to complete certain steps in the promotion in your Dropbox account.
For example, if the 2 GB is still showing, it is likely that the bonus has not yet been activated or the account has not been properly connected.

Hi skz, welcome to our Community! 

To activate the promotion, did you follow the exact steps in this article, by opening the pre-installed version of the Dropbox desktop application on your device?

Have you checked that your account meets the terms for the promotion? You can scroll to the bottom of the Help Center article in order to have a look at them.

On top of that, please make sure that you create a new Dropbox account through the Acer Jumpstart device installation process if possible, and complete the 2 steps of the Get Started guide.

Lastly, there's an FAQ section here with reasons for ineligibility for the HP promotion which would be similar for Acer too. Is it possible you're not eligible for some reason?

Let me know more, and we'll take it from there!