Believe it or not, the Amazon Echo has something similar to what your web browser history is on your computer: Alexa records and logs every single command you've ever given. Here's how to access it and see (and hear) everything you've ever said to her.
You might assume that the main screen of the Alexa app shows you past commands that you've shouted out. While this is partially true, the main screen is really only there to show you additional info for specific commands.
For example, if you ask Alexa about the weather, you'll see a weather card appear in the Alexa app, giving you more details about the forecast. If you set a timer, you'll see that timer appear in the Alexa app, where you can view the time remaining. However, saying something like "Alexa, turn the lights on" won't appear on the main screen.
With that said, here's how to see and hear every single command that you've ever told Alexa on any of your Alexa devices.
Start by opening up the Alexa app and tapping on the menu button up in the top-left corner of the screen.
Select "Settings" at the bottom.
Scroll all the way down to the bottom and tap on "History".
On this screen, you'll see a list of commands that you've given to Alexa, including all those times she misheard you.
Tapping on a command will bring up more options, like the ability to listen to the recording of the command (by tapping on the play button), sending feedback to Amazon about the command (by tapping "Yes" or "No" as far whether or not Alexa correctly understood you), and deleting the command from the history entirely.
Keep in mind that this section of the Alexa app is the only place where you can delete a specific command completely---deleting just the card on the main screen won't actually delete the command from the history, as it will still show up here.
If you want to delete the entire history of your Alexa commands, you can do so on a per-device basis by first visiting Amazon's website in your web browser of choice. From there, click on "Accounts & Lists".
Under the section "Digital Content and Devices", click on "Content and Devices".
Click on the "Your Devices" tab.
Directly to the left of an Echo device in the list, click on the ellipses button.
Click on "Manage Voice Recordings".
Click on "Delete".
Amazon warns that deleting your Alexa command history may degrade the voice recognition experience, since it uses those recordings to improve itself. So keep that in mind if you plan to go this route.