Ashamed

Don't be. Your body, your choices your past. No one else's, so nothing to be ashamed of. Now you have new choices to make, every meal every time. Not good, not bad, just what works for you and your body, and brings you closer to what you want.

It can be a bit very overwhelming for a while though, and trying to do it all at once is a recipe for failure.
I suggest logging for a while, even before making any serious changes to your diet.
Weigh (with a scale is best) everything you eat, and write why you are eating it (i.e, lunchtime, hungry, kind of bored, out with friends, watching tv) and how you are feeling right before, right after and an hour after (hungry, comfortable, normal, full, very full bloated, drowsy).
This gives you a baseline pattern for your normal habits and routine. From there, it's just a matter of experimenting. Are you very full after dinner? Cut back on a few things. Does lunch leave you bloated and gassy after an hour, try less or no mayo, and see if there's something you don't mind dropping each meal (fries, or cheese, or maybe only 2 tacos instead of 3).It's amazing how quickly these small and easily sustainable changes will add up to big calorie cuts. Only cut one or two things at a time, until they become habit instead if trying to do everything at once. That way they become individual habits instead of one big "diet". So when you backslide you won't drop everything at once, just one or two habits, that you can fix again more easily.