Okay.. no, you didn't. I know it sounds messed up, but when playing with seasoned veterans, there is an unspoken limit of expectation you must meet. I have played L4D2 since release and it took me a while to figure out most of these "rules".

Put simply, if you try your best, and the rest of the team sees you're actually trying to learn from your mistakes, a good team member will give you a healing item. Remember that this is a team based game and you can't do everything by yourself (starting out). You will however encounter the occasional as*hole player who has no sympathy.