No need to worry. As others have said airlock activity does not equate to fermentation and vise versa. I'd go a step further and say that once I got over my need to hear that airlock bubbling, I have switched over to open fermentations. Especially with top cropping yeast, all belgians and saisons. I'm not telling you this to persuade you to do the same, but once you see how many homebrews and professional are fermented in this manner, you'll see how unimportant getting a tight lid actually is.
I'd say no need to even replace the lid for future batches. The lid's only job is to keep bad stuff out, and any level of reasonable tightness is certainly enough for that. Air may be escaping around the edge somewhere, but that does not necessarily mean that "bad" air is entering. The one caveat I would give is that if you plan to keep you beer for a month or more for aging, I would make sure it is in a pretty airtight container to lower the chances of oxidation (but in that situation I would transfer it out of a plastic bucket and into something more suitable anyway).