The words "amateur," "hired," "friend," and "wedding" do NOT belong in the same sentence, unless you are prepared to later use the phrase "former friend."
If you want to take some "snapshots," swell. But unless you are experienced at shooting weddings, know the list of specific required shots to take, know how pose familial groups for formal portraits, understand how to shoot the ceremony without flash, have command of natural lighting and depth of field, and more, you have no business being the primary photographer.
Nothing personal against you, but this is a job only for someone with experience.
You should decline the offer and your friendship will remain strong.
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When I ask which Canon lenses are best,
people tell me to 'go to L.'