Don’t I get longer to pay if I file an extension?

NO!

Filing an extension does not give you more time to pay your taxes; it gives you more time to submit your completed tax return. If you owe money when you submit your completed tax return, the IRS will add penalties and interest for any amount that was not paid by April 15th – even if you have filed an extension. If you are going to owe money, you should submit a payment with your request for an extension to avoid being penalized for late payment and minimize any interest due.