This sounds like it might be fixed by setting the dashboard to be an exact size. By default a dashboard will always try and expand to occupy as much room as it is given, however in some cases it doesn't always look pretty when that happens.
In Tableau on the dashboard sheet, look at the bottom lefthand side and click "Edit..." and enter in an exact pixel height and width. This should hopefully solve the issue.
If I've missed the mark with my answer be sure to let me know. If you have something already published up to Tableau Public, you can always paste the link in your comment and I can look for myself to see what is happening.
I'm beginning to suspect that the problem is that the web page I'm embedding doesn't like being run in a frame. I did set an exact size, but as soon as the dashboard opens in the browser, the browser redirects to the actual web page itself, leaving Tableau all together.
I'll keep playing with it and let you know if I figure it out.
Thanks for the help!
And indeed, I changed the web page I was embedding and it works fine with a different URL. I suspect this probably varies from page to page.
Glad you got it resolved. Do you have the link to the misbehaving page? I would love to show it to our technical folks.
I didn't so much get it resolved as I did change it to remove the webpage
I'll put it back to the way it was when it didn't work and will send you a link to that when I get home this evening.