You should take it off. Keeping the humidity artificially high with something like your plastic cover provides perfect conditions for mold, which can kill your plant. If you take off the plastic cover, you might notice some of the leaves getting burned from the lower humidity, but your plant will soon grow new ones.
Be sure to read the articles on watering and sunlight for your new plant. In summary, VFTs need at least 4-5 hours of direct sunlight every day and they should only be watered with distilled water, rain water or reverse osmosis water.