I have multiple GMail accounts but none of which I use for travel. I just had United forward one of my reservations to a GMail account and I don't have the problem you have.

I'm using stock GMail through Google Chrome. No add-ons or anything else. It looks completely normal for me.

I suspect you might have a screen resolution problem - so it's not United or GMail related but just screen resolution related. Maybe try increasing your resolution to see if that solves the problem. Of course, you may not be able to read it then because the font will be too small You can always increase the zoom in Chrome.

-RM