Well, it does not matter what you or I think about the size of the collider but what the Unity engine “thinks” about it. In one of my previous posts, I suggested to tweak the values in the Physics 2D settings. Have you already tried that?
If all enemies can be hit by a bullet, you could write a simpler solution that does not involve any collision. You know the position of your player and the enemy. The bullet is probably intended to be fast enough, so the enemy won’t be able to dodge it. When you shoot at the enemy, you could decrease its health in the same method. The bullet could be an animation that fades away after a x seconds (or whatever your bullet is). Do the maths if necessary or use a hard-coded value. When you fire your gun, you could use Physics.Raycast to detect an enemy within the shooting range.
With 250,000+ students to support in the Unity courses, I’m afraid I can’t help out with issues that are outside the scope of the course meaning I do not have time to download and/or debug any personal projects. Please feel free to ask our helpful community of students for advice in our official Discord chat.