Can I make it on my bike?

Granted I'm training for my first half ironman next summer but I'd say you can make it if you put the work in and believe in yourself. Never underestimate the power in the mental game.

Yes, I think you can make it. Will it be as easy as if you were on a tri bike? Likely not, but I have no doubts you can finish it.

As far as what the lady told you, I suspect that what she was really saying was "I have doubts if I could finish on that." Trust in your training and you'll be fine. If you put the training miles in on that bike and get very used to how it rides and what quirks it has, you'll be fine race day.

I'm planning on doing a HIM this October on a 2014 Nishiki Maricopa. It's a Dick's-brand road bike (the only road bike Dick's sells) that I paid $450 for. I have no qualms about using it for the HIM. I'm not ready for the full IM yet and I won't attempt one until 2017 at the earliest (not traveling to any races next year, and no full IM near my location), but I'm not planning on buying a new bike in that time frame, which means I'll be doing the full IM on a bike that, from what I can tell given a quick internet search, is fairly similar to yours (read - an aluminum construction road bike). I have no question that I'll be able to finish the IM with it. I think you'll be fine so long as you don't let her comment get in your head on race day.

You will be just fine. What do you think they road in Kona before all of the fancy tri specific and carbon bikes? Plain old steel and aluminum.

I did my one and only iron distance (Vineman 140.6) on an entry level Giant Defy with some typical upgrades. No problem.

No reason why you couldn't complete it on that bike, I've seen people complete on much, much worse :p

It's really just going to be about your bike fitness and comfort, which can definitely come in that time.