I'm going to guess that you've been using AE for less than a week, and you're following some high school kids's tutorial on YouTube. You're just following a recipe, right?
You're not doing yourself any favors.
You need a firm knowledge in the basics so you have a feel for how AE works... to help you fill in the gaps high school kids tend to leave in the recipe:
It's not the fun stuff, but you won't get hopelessly lost as you are right now.
We're going to need a lot more information to be able to offer you much help.
Are you manually saving your project, or just relying on the auto-save when rendering?
Still seeing this issue, JonathanB? Let us know.