First sourdough loaf :) Need help...

The last week has been interesting, I made my first sourdough starter and then this weekend, I made my first loaf with it!

 A big thank you to Dabrownman, who gave me a great (and easy) way to get a starter going).

I didn’t used pineapple juice in the starter, just bottled water. I did have a bit of a battle with leuconostic bacteria during the first few days, but I just waited it out and the problem resolved itself.

 So here’s loaf number one:

I used the basic sourdough bread formula from the BBA.

I’m pretty happy with how it turned out, the taste is great! Not too sour but you can tell its sourdough. 

I do have a question about my crumb structure. As you can see from the photo, I ended up with a fairly nicely open crumb nearer the edges of the loaf, but it’s quite tight and dense in the centre. I shaped the final loaf in the evening and retarded it in fridge overnight. In morning it had flattened out a lot, so being a newbie, I decided to reshape it and tighten up the dough.(I let it ferment at room temp for about 4 hours before baking.)Was this my mistake? Should I have just left it and baked it as it was? 

i'm not sure why my loaf kind of exploded though, did i shape it too tightly?