It should be: "Malasado ang itlog kasi hindi ito naluto ng matagal" or "Malasado ang itlog dahil hindi ito naluto ng matagal." Both literally mean "the egg is soft-boiled because it wasn't cooked long enough."
The direct translation of the word "soft" in Tagalog is "malambot." However, if we are referring to food, we use the word "malasado" to signify that it is soft-boiled.
The word "long" is directly translated in Tagalog as "mahaba." But if we want to say "long time," we use the word "matagal."
Hope this helps. :)