will applying for deferred entry lessen my chances of getting uni offers?

I'd say the opposite if anything depending on your A level results. Unis often like people if they've already received their grades. But if you're retaking A levels I'd say your chances are the same as everyone else

i'd be applying through deferred entry rather than applying in my gap year, so not sure if this would have a negative effect seeing as they would have to be sure that i was better than all of the candidates applying the following year