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I’d echo what everyone has said above, and add that tapering varies. Completing every workout (of any IM plan) as prescribed in the last few weeks is not important, recovering but staying active is.
As it’s your first, it’s more likely that 3h30 is about half the time you’ll be on the bike on race day. With that context it doesn’t sound such a big session. On the other hand, if you’re elite level, 3h30 could be around 80% of your race day effort so you might even want to tweak that down.
Also, while you’re here check out The IM Thread 