My Refund Changed Miraculously!

So, I filled out my information on TurboTax as soon as I received my W2 from work, that would have been late January probably.  I was excited about it because it was the first year that I didn't have any income from side jobs.  My Refund was terrible, If I remember right it was only around 30.00 for Federal.  I hadn't submitted it yet, now this morning I'm entering in my piddly interest income from the bank, and I notice that my Federal Return is over 500.00???  Did something change somewhere?  Been using TurboTax for years, and never seen this.  Did I just start too soon?