If I saw this, especially if I were paying only as much attention as I typically pay to an app login screen, I would be confused about what exactly you were inviting me to do. The idea of try-before-you-sign-up might be sensible and novel, but the novelty is what makes it confusing. When I'm opening a new app for the first time that typically uses accounts, I'm expecting to create an account before doing anything else. This interface then surprises me. In other words, it's not the copy that's confusing, it's the concept!
The copy can help, though. I agree with other suggestions to just drop the user into the app without stopping on this screen at all, but if you're committed to the splash screen, change the big button text to just "New User". That makes it totally unambiguous where I, as a new user, am supposed to go.
For the same reason, I would remove all or most of the text above the button. Either it's not getting read, or reading is just instilling doubt as to where the button goes: "Wait, I'm trying to make an account, but apparently this will do something other than that, which requires explanation. Better not click there." You can allude to the sign-up not being immediate, but don't have more than one short sentence there overall. Like: "Explore [app name], then sign up!" This includes basic expectation-setting (this is where you go to sign up, you'll explore the app first) and omits extra details (you don't need an account, you'll be prompted to make one later).
Even that, honestly, is unnecessary. All the new user really needs to know is which button to press to start using the app. They'll discover immediately that they can explore the app without creating an account, and they'll be prompted to create one whenever you prompt them. If they're not making choices, they don't need to be told what's happening. They can see it.
If a new user does click on "sign in," is there a button there to create an account? If someone's that determined to have one already, let them!
Also, your dinosaur is cute. A+ dinosaur.