Making a decal gun

I’m trying to make a decal gun, like a paint gun. So far I have a crude decal set up, with ammo that will run out and not reload. But I’m not certain I have this set up correctly in the Material window. Currently, when a decal is shot, it shows up on both sides of the surface it hits. It’s also a flat square instead of an image. I’m trying to go for something similar to this video: /watch?v=NieITqWDcLM

How should I set this up (is it POSSIBLE to do) so that it shows up on one side of a surface, and is more like a splat shape? I imported a splat image, but it seems too big somehow (and it’s a really small file).

Thanks for any and all help! I’m really new to Unreal so I have a lot to learn!