There shouldn't be table tags unless you have added them yourself into the email. In a default, blank email, your text won't be surrounded by anything at all. If I add an image inside I can just highlight it and select "align -> center" and it centers the image.
I would like to see your email to see if there is anything better we could be doing in your situation. Can you email me a link to the email? firstname.lastname@example.org
I had the same issue but I use a token to fix it, its not the best solution but if works I just going to keep using it.