Does the fact that I take 20 and not 21 tablets of Microgynon jeopardize the effectiveness of the drug?

I've been taking Microgynon 21 for 17 days. Today I vomited unexpectedly half an hour after taking the pill and took another, eighteenth tablet from the blister. Should I finish the blister to the 21st tablet and take a week's break as usual? Is the fact that I will take 20 pills instead of 21 dangerous for me and I should protect myself again with alternative contraception for a week of starting the next pack?