Little Gem Lettuce - still no head

So my little gem lettuce looks like this almost 2 months after planting.

Little Gem lettuce after 2 months

The lettuce is tasty and growing well, so no complaints really, but this is the picture on the packet of seeds I bought, and what I was expecting the lettuce to look like.

Little Gem lettuce as per the Marshalls seeds packet

Pretty different huh?  Mine have pretty loose leaves and not in any way tightly packed.  The ones that should have grown are tight little heads of lettuce.  Perhaps they will still develop into something like this, who knows!

Here's another view from above to show the complete lack of any tightly packed leaves.

Little Gem lettuce 2 months after planting - view from above

The lettuces are definitely tasty, but I'm just left wondering whether I got funny seeds, the wrong seeds, or whether I'm just such a rubbish gardener that normal seeds grow differently to everywhere else when under my control.

Remember to click on the "Little Gem Lettuce" link on the right of this page or directly at the bottom of this post to see week by week how the lettuce has grown from seed to the date of harvest.