Planting Maincrop (Sarpo Kifli) Potatoes Chitting

I thought I'd give potatoes a go this year but realise I've left it too late for earlies (now mid April) so have today bought Sarpo Kifli maincrop. From what I've read I understand that earlies benefit from chitting but was wondering whether or not it was worthwhile with these main crop ones. 

These are the 15 seed potatoes I bought today from the garden centre but think I've probably got too many as my patch is only about 7' x 4' and if I made 2 rows they'd not be enough space between them. (I don't really want to grow in bags as I prefer to use the soil in the garden rather than be buying more bags of compost.) Would I be best off just planting one row instead of trying to squeeze in two?

I'd be grateful for any pointers, please...