I could never remember which side E was up to and would usually just stick him on the side that felt fullest and hope that I'd got it right Most of the time it was fine, I'd occasionally get lumps and very sore boobs which needed to be massaged or I'd hand express just enough to take the edge off (although you do need to be careful not to express too much or you'll increase your supply even more), but you'll find that this will probably happen regardless of any conscious thing you do, as babies will occasionally feed more frequently (growth spurts) or less frequently (starting to sleep for longer) and the supply/demand thing sometimes takes a while to catch up to what bubs is doing.

It's so easy to worry about being exact about times and alternating boobs when you first start feeding, but don't think that anything you've done has caused the situation, oversupply is sooo common in the early days. You're doing ace!!