Dreaded youtube embed issue

on a new post in my wp site, i can’t get a youtube embed to sit properly in the page. it shows up off center, and throws off the formatting for the rest of the front page. what’s odd is that in earlier posts, with code that looks identical in the code editor, youtube embeds have worked correctly! i looked in the forum archive here and see there have been various prob’s getting youtube embeds to play nice with wp. but i did not see this particular symptom discussed. anyone have this problem, or have any insight on this? thanks in advance.