You must make a definite contract of the voiceless /k/ with the voiced /g/.
Practice the following pairs of words using, wherever possible, one air charge for each pair: gate-Kate, goat-coat, got-cot, back-bag, Dick-dig, peck-peg, pick-pig, puck-pug, beck-beg.
Have your family hear you and ask them if they can tell your /k/s from your /g/s.
The sounds /s/ and /z/ are articulated by the tongue blade against the teeth-ridge, the tongue front being at the same time slightly raised in the direction of the hard palate.
