Why no gooey-ness?

I hate to say this or even admit it but there's this particular recipe that I've attempted twice and both times, I failed. BOO.

It's a gooey chocolate cake where the center of the cake should be gooey, almost like a molten chocolate cake. And both times I tried, there was nothing gooey at all. The first time I admit that I misread the recipe, so with the wrong amount of chocolate and 2 mins extra in the oven, I understand why it was not gooey with burnt edges. But the second time round, I did everything right, still not gooey and the taste was bitter. It was inedible.

And today I finally realise what went wrong. While shopping for chocolate I realised that I had bought dark bittersweet chocolate that had 71% cocoa instead of bittersweet chocolate that has 60% cocoa. Maybe that's why it was so bitter. But still, I don't know if that explains why I am not getting any gooey from the cake.

Now I don't know if I dare try it again for the third time. My poor lil baking heart can't take another round of non-gooey-ness. BOO.