Translation:It was not easy, but I cooked the eggs perfectly.
Not necessarily. It depends on what you're trying to say.
• It wasn't easy: adjective • It wasn't easily (done): adverb
I know it's not intuitive in English, but in languages like Polish it makes much more sense to use an adverb.
• To nie było łatwe = it wasn't easy • Nie było łatwo = it wasn't done easily
I hope that helps, I know it doesn't make much sense in English.