They are stretching quite a bit, and they are also quite small for being 3 weeks old... i suspect your problem is lighting, do you have any more detailed specs about the lights? (ie. colour temp & lumen output)

You said its more in the red spectrum, which kinda indicates its a lower colour temp (~2700K), in veg stage you actually want a higher colour temp (~6500K).

also, whats your distance between the tops and the lights? it certainly looks close enough, so I don;t think thats the problem... i have a feeling your problem might just be the number of lumens coming out of the bulbs, and it would also help if you have a bulb stronger in the blue spectrum.

I'd also be really careful about adding nutes to a plant that small... if you go stricty by the age of the plant, it can probably handle it, but like i said, they are pretty small for their age IMO.

Also, i;m not familiar with that MG soil, but alot of MG soil has time-released nutes and you may run into over-nuting problems by adding more to it... but if you are not seeing the leaves burn up, then you are probably ok.

edit: yeah, like the others also said, lose the drip trays... when you water them, just leave them in the sink or something to drip for 30+ mins before putting them back under the lights... if they are still dripping a little then, then just put a paper towel under them for another hour or something to catch anything else that drips out. the drip trays can keep the bottom layers of the soil very wet and mud-like, which will cause root rot.