I am a little confused. If it's a last minute job pick-up, isn't it even more important to complete them? After all, the scheduler sseemingly already went thru a cancellation and is in dire need to get this done. Today. So, cancelling this type of job - with or without emailing the scheduler - should be a no-no, unless there is an absolute emergency. One cannot accept such an assignment without being absolutely sure that it can be done. Very few jobs have a short time frame within which they can be completed. If necessary, I go to town twice to make sure I get everything done.
In almost 5 yrs now, I've "flaked" once, where I actually did the job, but reported too late, ie. after midnight, and got "banned" for it. It's an MSC that doesn't pay much, and to me not a great big loss. But it was a lesson learned the hard way.
My advice to the OP is, not to schedule any last minute jobs at all, since there seems to be a trend in "stuff coming up". Work with MSC's which let you schedule ahead, and make sure you stick to that schedule. Depending which MSC it is, they may give you a window of several days, and though you may have to pick a date, they may give you the option of CHANGING the performance date, not cancel it. If you have to cancel, because it is impossible for you to complete, it would be prudent to offer a make up date...
Then once you are more familiar and more effcient at this job, you can go back to pick up last minute jobs, and take advantage of possible bonus.
As all of the above posters said, this forum is an absolutely invaluable tool for everyone, but especially "beginners", and in particular those, whe started out alone and without mentoring.
Good Luck.
Kundry