I did a bit of investigating. Dahaha seems to be a verb, which means 'he spread out'. I'm not sure where the 'egg shaped' thing came from, but you're right, I did find one translation which used the term 'egg shaped'

I also found the following:
"And after that He made the earth shoot out from the Cosmic Nebula and made it spread out egg-shaped." ('Dahaha' entails all the meanings rendered (21:30), (41:11)). Translated by QXP Shabbir Ahemd**

Both translations had the following explanation:
** - Read with caution - These Translations, marked here with **, are considered either incorrect, far-fetched, non-conforming or misleading. Care must be exercised for certain verses or an alternate translation should be considered.

My conclusion, since dahaha is a verb, it probably has nothing to do with eggs, or shapes. The idea that God 'spread out' the earth is not specific enough to conclude that it is defining it as flat (or spherical for that matter).

It's true there are some Muslims who are overly enthusiastic about finding scientific miracles in the Quran, and will 'stretch' or 'spread out' the language in order to do so. To me, I am content with a Quran which does not openly contradict science.

Any language can lend itself to various interpretations. Look at the debates going around the U.S. Constitution.