I believe not enough light.

Many of the larger hybrids grow long leaves that may require staking or support of some kind... I usually wrangle my longer leaves with small hoop supports that I make from my husband's welding rod material... I bend it in half, then make a ring out of the top bent portion... I place the homemade ring support into the soil, making sure all the leaves are within the hoop portion... you can buy plant supports at some garden centers.

I usually abandon the coco disk that comes with the kits and use my own medium mixture... I use top quality coco coir as the base, and add vermiculite, perlite, a bit of sand, and horticultural charcoal as the drainage layer at the bottom of the pot...

Amaryllis, or hippeastrum, bulbs hate to be soggy and too wet... they like to dry out a bit in between waterings. Too much moisture will promote rot of the roots and the bulb, itself... and if the planting medium holds moisture too long, or the plant isn't getting good drainage, the roots and bulb could possibly rot.

They also require a good amount of light for proper growth of leaves... if they don't get enough light, the leaves will grow longer and leggier than they should, and be lighter in color...

Without seeing a photo of your bulb, I can't tell what exactly has contributed to your leaves all laying over, but the above are things that might be factors...

I hope I given you a few things to consider... if you search here in the forum, you'll find all kinds of great culture information...

Good Luck!

Oh!

Fresh leaves which arte not covered and thus partly supported by older leaves grow straighht upwards and they tend to collapse suddenly!
This does not necessarily índicate a deficiency. It IS very likely when leaves grow so fast!

Support the leaves with sticks and adhesive film. Keep a steady vigilance on their growth behaviour and be ready to intervene if they become unstable!