I understand the difficulty of getting side scrolling to work on Unreal engine, as I have recently done 3 side scrolling projects. 1 using the premade side scroller in 5.6- highly do NOT recommend- caused way more issues than time saved. They all proved difficult/ finicky with the camera, rotation and controls. I ended up just setting rotation of the character depending on what direction they have pressed. I'm not sure if your character or enemies are constrained to a plane, because some of the first enemies seemed to be further back and unable to kill. Another small performance booster would be to set life span of the Bullet BP on begin play. This would limit the calculation for their movement and the number of actors in the world. When stepping backwards at the beginning and being shot at the end, player control is taken, and the camera is switched.
The bullets work and map had a great start. Your image for the cover is also really cool! Great work especially for the time allotted! Did you use AI?

You did a great job!