It was very different from my other phone.
What was different about this phone?
It was way smaller than my other phone and I hated it.
It's okay to find out that you don't like something after you bought it. Check the store policy where you purchased the phone, since they may give you a certain period of time in which you can return it.
No, I don't have time for that.
I'm sorry to hear that you don't have time to make an exchange.  Since it is probably necessary for you to have a phone, you may just have to get used to the smaller device.  You will probably be able to upgrade again fairly soon.