Last saturday morning I get a phone call from this lady, who I never done a cake for, asking for a cake for next Saturday. She told me what she wanted and how much it needs to serve. I was kind of hung over from the birthday party I went to the night before. When I got off the phone, I looked at the paper I was writing on. I under charged her by $30. I'm going to honor my price I gave her, but I need her to know that I messed up and I'm not that cheap. My BF said that I should say something when I give her the cake. I just don't want her to order again and think the price will be that low.
Yes, definitely let her know. I'd just tell her when she picks up the cake, that you were distracted when she first called and accidentally mis-quoted the price, and you just wanted to let her know for future reference or referrals, that a cake of this type would normally be $xx.
I've done that several times, when I've give them a free upgrade because I want to try something new, or realized I might need to make a size bigger that I originally figured to achieve the proper look/proportions, or didn't realize how time-consuming a project was going to be when I priced it out.
Print up an invoice reflecting the price it SHOULD have been, and then note on the invoice the $30 "discount" (or however you want to phrase it--even if you note that it was made in error).
Anytime anyone gets any sort of discount from me (be it an error, a legitimate discount, a favor, whatever) I make clear note of it in their invoice so they see exactly how much of a favor I am doing them 
Even when I donate a cake for charity there is an invoice as to how much the cake SHOULD have cost (for my tax purposes, and theirs).
I dropped off the cake Saturday. I told her what CakesByJen2 said that I was distracted when she called. I told her my normal price. She totally understood. She wanted to pay the rest of the amount. I told her "no, I'm giving you the price I told you on the phone. I just telling you this for future orders." She was so happy cake, that she wasn't bothered by this at all.
Thanks for the advice!!
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