Why am I paying short term capital gains of 37%?

before entering my short term capital gains to Tax Turbo, I had a refund of $1,821 from Fed, $78 from from State. After entering my short term capital gains of $17,334, I ended up owning $3,059 to Fed, $1,482 to State, wondering if I'm paying 37% tax from my gains? (something like 28% to Fed and 9% to State)I'm filling married filing jointly, with 2 young children, zero exemptions on both of our w-4. AGI of $120,271 including my capital gains. I mean, I know that the calculation is right because this is straight from the Table/worksheet, but the part I don't understand is why there is so much difference between A. before entering my gains and B. after entering the gains. Can someone help me?