Not sure what you were trying to do. Were you trying to include an image in the email, or were you trying to open that Sony app (program) separately, and instead the app got attached to the email? Were you planning to add an image from that Sony program to the email, but selected the entire Sony program instead? Or....??
Is there an icon for the attached file in the body of the email? If so, just place the cursor to the right of that icon, and hit the Delete key.
Or even simpler, just delete that email, and write a new one.
At this point, because you probably chose the wrong file to attach and pressed all sorts of keys in hopes of fixing things... I'll wager that the Mail app needs to be force-quit. Press the Command, Option, and ESC keys to open the Force Quit window, and find Mail in the list of applications. I wouldn't be at all surprised if Mail is listed as "not responding." If it is "not responding," highlight Mail, press the Force Quit button, and restart Mail afterwards.
