Should I tell him im not comming after all?

So im currently trying out different combat sports at this new gym. Im allowed to tru outpst of the sports before deciding if I want to continue going there or not.

I haven't signed anything yet or anything, but I was there yesterday and the leader and I had an unofficial agreement for me to join a kickboxing class today.

I dont want to go today, but im unsure if I should tell him or not.. there is no signing up to classes so you could say he's the only one Who expects me to show up.

Should I tell him im not comming?
Should I tell him im not comming after all?
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