You have Two Hands
You have two hands, and it’s not just so you can hold a leash AND treats- remember you have two sides!
Work your dog off both sides at every level of training. That way in a trial situation it will not be startling to your dog when you switch sides. Practice heeling on and off leash from both sides. Personally I have found that ‘heel’ for left and ‘side’ for right work beautifully for my dogs. I also tilt my head to where I want them to be as an additional cue.
Ask your trainer or agility friends if they notice you being unclear in body language about where you want your dog to be if you start having problems. Double pointy hands can happen so easily, to anyone, at any time!!!