Baking soda and vinegar rocket

Materials
soda bottle
scissors
baking soda
vinegar

Results
Perplexing

Working theory
Combining baking soda and vinegar creates a large amount of carbon dioxide gas, causing the mixture to expand and bubble out of the container. If we can direct that pressure downward, we should be able to propel the container upwards.

Experiment
We took an empty soda bottle and used a scissors to poke a hole in the lid. We put a good amount of vinegar into the bottle and filled the cap with baking soda. After our safety goggles were on we put the cap on the bottle and shook it up (with a finger over the hole). We placed the bottle on the ground, cap side down and stood back. Although the bottle became very pressurized and a bubbly stream came shooting out of the hole, we didn't get any lift. We think that either pressure was going out of the edge of the cap, near the threads (aimed upwards) or the cap wasn't flush against the ground, causing the pressure to go out at an angle.