CO2 gasses will escape through the path of least resistance. If your airlock does not fit tightly around the mouth of your fermenter the gasses will escape around those edges. It is really not a problem. The bottom line is that bubbles in the airlock is not a true indicator of fermentation activity.
It takes very big mistakes by the brewer to stop beer from becoming beer. If you made a decent wort and you add reasonably healthy yeast then you will get beer. All it takes is patience.
There is a gentleman who is often called the Godfather of homebrewing. He was holding classes in his kitchen long before homebrewing in the U.S. was even legal and wrote a book that was (and for some still is) considered the Bible of homebrewing. His name is Charlie Papazian and the book is The Complete Joy of Homebrewing. I only mention all of that because there are many new brewers in the hobby who are not familiar with Charlie these days. Charlie made famous a philosophy which says; "Relax, Don't Worry. Have a Homebrew". If you missed your OG by 3 points... relax, don't worry. If the trub from the boil kettle gets sucked into your fermenter... relax, don't worry. Have a homebrew and if those little things matter to you just try and do a little better next time.