At least make it more blue to make it look like a real tattoo...

nice idea, but looks a little flat on your arm. I have multiple tattoo's on my arm and back and going from a flat image to your skin there is that gentle curve to your body that can be seen.

the curve looks better.

change the layer style of the cross to overlay and lower the opacity

The lower part of the cross seems a little bit floating ... I think maybe you can play with the layer style and opacity like RickLaMesa said. And maybe try to use the liqufy to fit the tattoo better with the skin.

This doesn't look like a tattoo, try experimenting with blend modes such as overlay or multiply.

try to get a dark green color, most tatoos are that color.

nice try author. like the changes you made.