It sounds like you are suffering from the common ailment of buyer's remorse. Don't worry, you made a good purchase.
Consider this: It looks like a used version of the lens is selling on Adorama for just a little less than $100 under the new price. It would have cost you more than that to rent the lens for a month.
So, even if you decide not to keep it, you won't be out that much money.
Also, keep in mind that it wasn't that long ago that lenses didn't even have IS. These days we all act like IS is essential, but we used to shoot all the time with non-IS lenses and never even thought about it because it wasn't an option. Use the lens, enjoy it and think about all the other goodies you can buy with the $1,000 you didn't spend on IS.
If you decide later that you absolutely have to have IS, then you'll be over halfway there when you sell this lens.