the plants are all still stretching - should i just fill in some more soil around thier bases???
HPS lights used for vegetative growth will cause your plants to stretch - there's nothing you can do about it except switch to a MH or 6,400k CFL.
Your plants will stretch regardless of how far the light is away - and a 400w HPS 12 inches away from seedlings breaking the soil surface 2 days ago IS TOO CLOSE REGARDLESS OF WHAT PEOPLE ON HERE HAVE MISTAKENLY TOLD YOU! That light should be at least 3-4 feet away from those plants at this stage in their growth - having it any closer will not stop the stretching.
Seedlings and rooting clones only require about 500 lumens per sq foot - that HPS is putting out 50,000 lumens at 1 foot distance! There's very little photosynthesis going on at this stage in their growth - most of the growth is happening below the soil surface - so why do you need so many lumens on the plants?
Your best bet is to get an oscillating fan on those stems as soon as practical to start thickening them up and depending on how bad the stretching is - when you repot them bury as much of the stem length under the soil as possible - it'll just form part of the root system.
HPS is not an ideal light to veg under for this very reason - I've forgotten now how many times I've said it but still people take no notice.