I havent seen the recipe, but if it is a cake/muffin recipe then the centre shouldnt be like a quiche.
Generally speaking it may have been too moist due to excess water or milk/cream content. As I said, havent seen the recipe, can you link it and I will have a look and give you a better answer.

The other thing is how you mix a muffin or savoury cake. They should only just be combined. Not like a cake batter, if you catch my drift. So a little less liquid and less mixing. Check your oven temp too. this will have a massive impact, particularly if you are opening the oven during cooking

Sure that doesnt help all that much, but if you link the recipe or copy it here I can give you a better answer! lol

Although, if it was yummy....