bleed thought under mask

can anyone help me with bleed through  every time I try to airbrush the white trim on my Cutty Sark  I get a bleed though I don't know what Im doing wrong when I  mask off the Hull using tamiya tape and even barnish it against the  area that will be painted  It keeps bleeding though should I use a another brand of masking tape or am I airbrushing it wrong Im  aiming right at  the area to be painted  left to right or right to left   I would apprecate any help any one  can offer-thank you

                                      Ronald