use the ruler to see if the cross is right, then use the knife to cut the cross out of the cardboard.
Lay a other cardboard underneath the shirt for bleeding!

Make sure cross is in the centre and the shirt without folds. stick with tape your cardboard on your shirt.

Grab your paint and sponge to paint. note that you still need to hold or push the cardboard down since it can bleed out a little.

Paint the shirt al over and make sure that there is no paint bleeding anywhere. If it did, grab a towel with warm water and gently rub it off.

repeat this steps 3 or maybe 4 times (depends how solid it must look). Each time you leave it to dry for 10/15 minutes, it can depend on your paint how long it need to dry.

When your finished leave it to dry for an extra hour. Then gently remove the cardboard and tape.

you can see I got some bleeding here and there.

NOW! wash it, make stupid faces while making pictures and your done!