That's why you have a condition say something like "check player angle"
-If control "shoot" is pressed
-If player angle = 0
---spawn bullet at image point "bulletspawn"
---Set bullet angle to 0
-If control "shoot" is pressed
-If player angle = 180
---spawn bullet at image point "bulletspawn"
---Set bullet angle to 180
Really, all this stuff is covered in the "Ghost Shooter Tutorial". Look it up on scirra.com's tutorial page, and trust me, you'd learn a lot from it.