Congrats, that's a very good time, especially if you didn't "train properly" as you eluded to in your post.
I'm about to run my first HM in 2 weeks and did my last long run today. 21 km! Yikes, I was talking to myself for the last 3km...You know, "C'mon Kim, you can do this, one more foot in front of theother...Keep going, you're not gonna die from this...Well, maybe not DIE, just collapse in a heap on the side of the road,...HEY, stop with the negative talk. Look, it's time to walk again, Youre gonna be fine..."
I'm sure all you HM runners are familiar with the above, or am I the only crazy lady talking to herself and barely running, and almost home? LOL
I'll let you all know how it goes. I expect a 2:40 finish time but really don't care. I just want to FINISH my first HM at 50 years old! (Upright and smiling if possible!)