It’s nice how I can fix my own problems …
Here is what I found: my template width is actually 1000px instead of the 960 that I stated above in the original question.
I edited my mega.css as such:
.ja-megamenu {margin-left: 140px; padding: 0; width: 840px
}
Notice that 140 + 840 = 980 (don’t know why the 20px difference in what I did and the width of my template). I tried percentages and they worked in Firefox, but were different in IE and Chrome. I tried a lot of different variations and they would work in one browser but not the others.
This solution actually works in all three. I am open to better solutions if someone can offer them. I am a total rookie at this but I am a master tinker. Got a better code? Teach me. I’m open.