Crib Mattress- Snug at Sides But Not at Head and Foot

ncjulia12

I had no problem picking out a crib (Ikea Gulliver) but spent hours and hours researching mattresses and then just now finally ordered the Colgate Eco Classica I Crib Mattress.  

I was so excited for it to arrive today and put it in the crib to test it out.  It's very snug against the long sides, but loose at the head and foot sides- I can stick my whole hand between the mattress and crib.....

I looked at the specifications on the crib and apparently my mattress is .05 inch shorter than recommended.

Do I really need to mail this mattress back to Amazon?