While we in this forum have no access to your personal tax return, a very good thing, the most common reasons to owe tax come April are: (a) your paycheck withholding allowances were a bit too high, or (b) that you had income that wasn't included in a regular employee paycheck, for example self-employment or investment income. There is also the possibility that you might have owed extra tax because you weren't covered by health insurance for some or all of the year.  Self-employed people get hit with extra social security and medicare tax.

If those are not the case, double check your return to see if you put in the wrong information, for example typing some number with an extra 0 or transposing two digits.