Its hard to get cedars that are straight, you can straighten them a few ways.
#1 is with a screwdriver, Guru shows this in the How to Section on the main page.
#2 is if its a slight bend just roll it on a flat surface and identify the arc in the bend. The put your thumb on the highest point of the arc and bend it slightly to remove the bend.
#3 You can face two chairs back to back(about 18-24" apart) and find the arc and use a shower curtain hook with some weight on it(lead fishing weights,ect) and hang the hook on the arc and after some time it will straighten out.
Hope this helps.Tim