I agree, a 12 gal is too small for even one goldfish (20 gal is suggested for one as they can get fairly large and are very messy). Neons are small but active and would prefer more swimming room than that tank has. You could do:
1. two dwarf puffers OR
2. a school of 8 nano fish like ember tetra, chili rasbora or celestial pearl danio. Some endler's livebearers are also an option. You could have your shrimp as well and a small centerpiece fish like Scarlet Badis or sparkling gourami (none of the larger type of gourami though) OR
3. One betta OR
4. two-three platy and the shrimp OR
5. Some guppies and the shrimp