Having a leak isn't a problem in the least. Airtight is not a requirement in any way! Many folks just cover their primary loosely to prevent anything falling in and let it go.
You may have created a problem by racking it at the height of fermentation. You certainly gave your yeast a set back but hopefully it will recover and finish its job. Next time, leave it alone for a few weeks and trust your yeast to know what it's doing.