In this case you don't need to decline, wait until the last day (but be careful not to miss the deadline) and then submit a LoE instead of the PCC explaining that your PCC did not arrive but it has been ordered (include the evidencie you have ordered your PCC from ACRO, that is the tracking number, ACRO email confirming your order for PCC, etc.) and state that you'll submit it via CSE as soon as it arrives.
However, if you'd prefer to decline the ITA and wait for the next one you can do that, but there is no guarantee that the CRS in the next one will be low enough for you to get another ITA.