When you create a poll, you can limit the number of votes allowed per social profile.
Go to Marketing Activities.
Select the poll, and click Edit Draft.
In the poll editor, go to App Settings > Advanced Options.
Check the option to impose a Vote Limit and enter the maximum number of votes allowed.
You can click Finish > Approve and Close to publish your poll, or you can continue customizing it. For example, try configuring the after-share prompts.