How do I get over of being afraid to help my grandpa?

We aren't very close, but we get along great. I was over a little bit ago to visit my grandpa, and grandpa with my mom, and he asked if I could help him take apart an old deck tomorrow. I said yes, but I'm terrified, because he does get frustrated rather easily. Not with me really, but I've seen it before when he's interacting with other people. I also lack common sense, and make stupid mistakes, and I'm afraid he'll go off on me. How do I get rid of this anxiety?

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8 mo
Grandma, and grandpa. Not grandpa, and grandpa.
How do I get over of being afraid to help my grandpa?
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