If you want to base your pregnancy on your LMP, it is never accurate even with a regular menstrual cycle. The only accurate ones is when you do an ultrasound. That's when the fetus is measured and your EDD is estimated. So yes, it is totally normal to be earlier or a bit later than you've guessed ☺️
Not at all:) the LMP is only an estimate. The official dating scan is more accurate:)