This is from Netdoctor:
Yasmin info from Netdoctor
What do I do if I miss a pill?
You should try and take your pill at the same time every day to help you remember to take it. If you forget to take a pill, you should take it as soon as you remember (even if that means taking two pills in one day) and then continue to take your pills, one every day, as normal.
With Yasmin, if you have missed ONE or TWO pills, you will still be protected against pregnancy and you don't need to use extra contraception. Take the last pill you missed as soon as you remember, then continue taking your pills, one every day, as normal.
If you forget to take THREE or more pills, you won't be protected against pregnancy. You should take the last pill you missed as soon as you remember, forget the other missed ones and then continue to take your pills, one every day, as normal. You should then either not have sex, or use an extra barrier method of contraception, eg condoms, until you have taken a pill correctly for next seven days in a row.
If the pills you missed were in the third week of your packet, you should skip the pill-free week and start a new packet straight away.
If the pills you missed were in the first week of your packet and you had unprotected sex in that week, or in the pill-free week before, it may be recommended that you take emergency contraception (the morning after pill). Ask for medical advice.
If you are confused about any of this, you can get individual advice for your circumstances from your doctor, pharmacist, local family planning clinic, or by calling the fpa helpline on 0845 310 1334.