Using too much baking soda or baking powder can really mess up a recipe, causing it to rise uncontrollably and taste terrible. But don't freak out if you accidentally poured in more baking soda or baking powder than you intended. Depending on the situation, you might be able to fix it. If you can't, dumping all the ingredients and starting over is your best option.
An Easy Fix
Just increase the other ingredients in the recipe to match the amount of baking soda/baking powder that you used if you know how much extra you added. For example, if you accidentally used 1 teaspoon rather than the 1/2 teaspoon the recipe called for, just double all the ingredients in the recipe and you'll have a big batch of whatever it is you're baking. Then proceed with the recipe as written. If you can, increase the ingredients enough to create another full recipe. This may require a few tricky measurements and conversions, but it'll save you from having an awkward portion that is either too big or too small for your pan, or that requires a special oven time.
This isn't a perfect solution since it will give you a larger batch than you intended to make and might require an extra pan or cookie sheet, but it sure beats tossing out all of those ingredients.
If You Haven't Stirred Your Ingredients in Yet
If you catch your measurement error before you start stirring all your ingredients together, you might be able to simply scoop out the baking soda/powder and start again. This method will waste a bit of baking soda or powder, but it'll allow you to save the rest of your ingredients. Don't try to guess what the right amount would be on what you added to the mixing bowl; it is better to remove all the baking soda or powder and start again.
Can't Scoop It All Out?
If you have no idea how much you threw into the mixing bowl and you can't scoop it all out, tossing your ingredients out and starting again is probably your safest and best bet. While it's painful to waste ingredients, you probably won't be happy with the way your recipe turns out if you decide to move forward with your recipe without dealing with the overdose of baking soda or baking powder. And the only thing worse than wasting ingredients is wasting ingredients and time.
Baking for Guests
When you're cooking for the family, flops aren't a big deal. But when you're cooking for other people, you want your recipe to turn out right. If you're making something that you won't be able to taste before serving and/or won't have time to make again, the smart money is on just starting over when you realize your mistake. You want to be remembered for your baking successes—not your baking flops.