The controls are a bit of a challenge! I included it in my Open Jam 2018 compilation video series, if you’d like to take a look. :)
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Indeed the controls are part of the challenge, but more than that they are misunderstood. :)
Spamming the move keys like you are doing is only beneficial at top speed. To speed up timing is important. After you've gained some speed you can easily out-swim a jellyfish. Hopefully this video will make it more clear: