First of all, Relax. This too shall pass. As to your current problem, go see your mom. It's no insult to ask for the reciept. You can tell her how much you appreciate the gesture but how you need a different style of knife. Your mom wanted you to have a knife. She had no way of knowing the knife would have to be specific. I'm sure she'll be understanding. After all, she still bought you the knife, whichever one you end up with.
By the way, not having the proper tools doesn't or shouldn't put you on the edge of being fired. The kitchen should provide the proper tools, certainly something as basic as a utility knife. If they can't or won't provide a simple utility knife for you to do the job you were hired to do, you should find another job. As time passes collecting your own knives is commendable and convenient but if you are just starting out in the industry, having your own knives should not be a job requirement.
By the way, not having the proper tools doesn't or shouldn't put you on the edge of being fired. The kitchen should provide the proper tools, certainly something as basic as a utility knife. If they can't or won't provide a simple utility knife for you to do the job you were hired to do, you should find another job. As time passes collecting your own knives is commendable and convenient but if you are just starting out in the industry, having your own knives should not be a job requirement.