How do I throw up the M&M's I just ate?!

Insert finger in throat

Unless you had an excessively large portion size &/or by eating those M&Ms you exceeded the daily total calories required to maintain your current weight, you have nothing to worry about.
There is no such thing as a "naughty' or "forbidden" food, just as long as your daily eating plan is balanced & you pay attention to the portion sizes of what you eat.

And if they did make you exceed your daily calorie allowance, there's no need to damage your health by making yourself throw up. It takes 3500 excess calories to gain a pound of fat & I doubt that you ate that many M&Ms.
Do the sensible thing & make healthier, less calorie-dense, food choices the rest of the day and perhaps do a little bit of extra exercise

P.S
Peanut M&Ms are yummy. I wouldn't mind eating a few of them right now :.)

If you're just gonna throw them up why did you eat them?

Don't throw it all up. Live with it and go work out this week.