Granny square too 'square'

I used to crochet a lot as a child (although I never did finish my 'snail' blanket, as I called it). I have recently started crocheting again so I can make a baby blanket out of granny squares for by best friend's first baby.
I have been making a couple of trial squares to get back into practice and it seems a little 'square'.

I seem to remember that each set of three dc's was almost shell shaped, small at one end and larger at the other, but in my trial squares they are all pretty uniform. I have tried changing hte number of chains between sets of dc's to no avail - is it perhaps the size of the hook or the weight of the yarn? Or did I imagine the shell shape?

Thanks for your help.