Is your forum at this URL?
http://getyochaton.weebly.com/forum.html
I just checked it in IE6 and FireFox and they all look fine. Which browser did you use when you see only half of the forum loaded?
Also, I noticed that you have a dark background, and your forum uses the default white background. You may want to use Options->Editor->Change Appearance..., then on that page, scroll to the bottom the "Look & Feel" section to choose the dark one, then click the "Save changes" button, this will change your forum to become a dark background and will fit better with your site.
Another suggestion is that you don't need to place the forum inside a blog post element. The forum is supposed to be in it's own page. With weebly, you can simply create a new page, and then drop the nabble forum element into it.
Let me know if you have any questions.