Why are you having an existential crisis? You should be enjoying life to the fullest. Not many people have succeeded in escaping the drudgery of religion. Keep this text in mind whenever you feel envious of christians who seem to have a life of purpose:
"If in this life only we have hoped in Christ, we are to be pitied more than anyone." - 1 Corinthians 15:19
Paul was saying that without the future eternal life that christians hope to have by a resurrection, christianity becomes a pitiable waste of ones life. From your atheist perspective, that truly is the case! Think about it: millions of people around the world are living pitiable lives - wasting the only lives they have on a myth that isn't true; foregoing higher education; subjecting themselves to ridicule and persecution; foregoing a loving relationship with that soul mate they met just because they're not of the same religion; wasting sundays listening to boring sermons; foregoing perfectly harmless entertainment; feeling guilty about enjoying too much of the pleasures of life. A pitiable life indeed!
Why does there have to be an overarching purpose to life imposed on you from the outside? Religion implanted that notion in you to make the drudgery or worshiping a higher power seem appealing - like your part of some grand scheme bigger than yourself. Well, actually you are part of something much bigger - but its not some supernatural intelligence. You are a part of the universe; you are part of the fascinating concept of the universe attempting to understand itself. You will never become worm food. Only your body will.
You can make a difference in the world. You can give meaning to your life. Today we are standing on the shoulders of those who lived before us. Their lives certainly had purpose. Everyone contributes something to humanity that has a ripple effect that lives on long after they're gone. Just try you best to make positive ripples and have an enjoyable life.