Please post the code you are using in between backtick ( ` ) characters (backtick in on the key next to the #1 key ie. the same key as ~ but in lower case) here so we can examine it and hopefully reduce the width.
The narrow version of the polls is 150px wide and your sidebar is 174px wide, so there should be no problem. Perhaps you switched the size to Narrow after creating and inserting the poll, and either forgot to click Save or checked the result too soon (if you edit a poll, it takes some minutes before the changes show up). Try again please and leave the poll on so we can check too.