Hi,
You will probably want to clean the cage and possibly even the snake afterwards whatever the outcome - use damp paper towel to try and wipe the worst off the snake but if it is really stressing it out then stop. You really don't want to freak it into a regurge.
Rats shouldn't burst though so either it was previously defrosted and re-frozen or you need to change your defrost system a bit.
It might be an idea to use the weights to judge prey as well as the "no thicker than the widest part of the snake" rule though.
If the snake hasn't eaten for a while smaller meals are a good idea for the first few feedings.
dr del