Held up in a parking lot, could I have used a weapon?

Not sure if this belongs here, but here’s the situation. I am a young female who just moved to a city. Yesterday, as I was unloading groceries into my vehicle, a large man came up behind me and blocked me between the cart and my car, and demanded my purse. He threatened to kill me several times, and held something to my back from under his sweatshirt, but I’m not sure that it was an actual weapon. I don’t carry a purse, and repeatedly told him I don’t carry cash, only a credit card. Eventually, after realizing he wasn’t going to get anything from me, he walked away.Since moving here, I’ve been thinking about getting a handgun (I’ll obviously get some training etc. before carrying it). Had I had one, would I have been justified in using it in this situation, since I didn’t actually see him carrying a weapon? Also any suggestions on type to get? via /r/CCW http://bit.ly/2s0Ghof