Why am I being taxed at a blended rate of 36% on 37,000 of taxable income?

Did you by any chance have insurance through the marketplace and are having to pay back the Advanced Premium Tax Credit?  If so, this would be added to the amount of the blended tax rate.  Otherwise, your blended rate should be around 27% if you ONLY have $37,000 of taxable income from self-employment.  This would include about $4,200 in federal taxes and $5,661 in Self- Employment taxes which are 15.3% of your self-employment income. This would come out to 27%.  

If you did not have any other credits you had to pay back, you can double check your entries and look at your 1040 to make sure all the numbers make sense.  If they do make sense, then the blended tax rate will not affect your return.  This is not an  actual number that the IRS uses.