Here is the full list of all 13 Summer Catchers Demo achievements.
Activate a secret code
Listen to the whole inventory song
Receive the Bell
Complete tutorial
Play in co-op
Overcome a hill or a bridge. No boosters, no bubbles
Chew some bubble gum (co-op only)
Break down a car before a race (co-op only)
Leave a race right after a crash
Collect 1000 mushrooms from totems
Collect 1000 rainy mushrooms
Overcome 5 obstacles in a raw in a bubble