It sounds like you might've gotten caught by the mathematics of your income this year. You must meet one of 3 hurdles to avoid a tax payment penalty. You must:
1 - Owe less than $1,000 when filing your current year tax return;
2 - Have already paid or had withheld at least 90% of your total current year taxes due;
OR
3 - Have already paid or had withheld at least 100% of your total taxes due for last year.
If you failed all 3 tests, then you are subject to a tax penalty.
