Hello, you should try to plant the seed as soon as the white root first appears from the seed and not leave it unplanted for so long that the leaves are already showing. You need to keep the seedling warm, around 20-25 degrees Celsius, but humidity is not really required, as it can cause problems with mould and fungus. Leave your seedling in the open air and not covered with a cup/bottle/cover of any sort. Only cuttings/clones need extra humidity, because they have no roots at first.
At this stage, plant this sprouted seed as soon as possible, the root needs to be in darkness, otherwise it will die. Plant it into a roughly 500ml - 1000ml container to get it started. Once this seedling has 4-8 sets of leaves, you can then transplant it to a larger pot.
Hope this helps..... Organoman.