Kill or cure - yellow leaves from day 5

Sorry for your loss. Your plant dying is probably the result of having been covered with a plastic beaker for four days. Cannabis is not a rainforest plant and does not require artificially high levels of humidity. The high humidity has probably provided the ideal for fungus to grow and this fungus has transferred to your plant, causing death. Also, plants need good air circulation, not only to strengthen them, but to also provide them with carbon dioxide and remove excess moisture from the leaves. The brown marks were undoubtedly caused by fungus and once the fungus gets into the stem, it is bye bye seedling. In reality, only clones/cuttings need extra humidity, because when freshly taken, they do not have a root system to provide them with water. Next time, keep the seeds moist and in the open air, just like Mother Nature has done for 100s of thousands of years and they will be just fine. Good luck and happy growing! ,..... Organoman.