mat leave and tax question!

Kylie
I have been told I will owe. Large sum when I return to work, and have become super nervous!! Daycare costs will run us tight and I have no clue how I will be able to repay a huge sum of money to the government if I needed to! 
I have been on Mat leave December to December, so an entire tax year.  I had top up form my employer totally $5000 for the first 6 months. My ei totals around $22000 for the year... 
Has anyone not owed money at the end of Mat leave?! 
I have no RRSPs and am not eligible for tax credits to offset it... I'm wondering what I should expect to pay back... 
Anyone have experience or help or advice for me?