If you go over the transfer balance cap, the ATO will let you know that you need to remove the excess amount, plus any associated investment earnings, from your Retirement Income account. They'll also apply tax on those earnings – see the PDS for more information on this.
You won't be considered as having gone over the cap if your Retirement Income account balance grows to more than $1.9 million due to investment earnings.
If you're concerned that this limit might impact your retirement plans, you should think about getting financial advice.