How to stretch my Page?? Please CSS experts

Hi
Im kind of newbie on wordpress, here is my blog: lbow.com.br

Im using one iframe from external site, see image below:

https://i.gyazo.com/0e7d3b18a479d97acc148d890cb59682.png

This iframe looks like bigger than my template, I using showcase template, I would like to stretch this template in order to fits my iframe in total

https://i.gyazo.com/bc54a94a502906283d830cc8801ee569.png

anyone can help me? thanks