This has popped up a few times this morning, so I'm just going to make a thread - anyone else feel free to add anything I forget.
I didn't get the guaranteed ATAR! What now?
The guaranteed ATAR is just that - a guarantee. If you get that, then great! No need to worry - you'll get an offer. If you don't get the required ATAR, You can still get an offer. You're not guaranteed an offer, however Melbourne/Monash will still consider you (and your SEAS points) when giving out offers! So if you want to enrol in a course but missed out, then leave it in your preferences. You may still be given an offer in first round or subsequent rounds based on your selection rank (ATAR+SEAS+bonus points=selection rank).
It is worth considering including courses in your preference list that have a lower entry requirement in case you miss out, but don't remove a course that you want just because you don't think you'll get in!