Consuming somthing not halal

We live in a non muslim country. My parents bought a cake that had gelatin in it. Before eating I checked the ingredients and it said that their was gelatin in it. I asked my mom about it and she said that my dad bought it so it must be halal. The next day we were having the cake and once again I asked my mom if it was halal she asked my dad and he said that he didn't check the ingredients because he didn't think a cake can have gelatin or something like that. I feel horrible about this. Is it my fault that I ate it?If so how do I repent.