A little before leaving for the date, txt her something like "running a little late today, I'll be there at [give some time slightly after the agreed upon time]". This implicitly confirms the date, gives you an excuse if you turn out to ACTUALLY be a little late, and all without having to explicitly confirm (which would give her an easy out).
From personal experience, I've found it best not to let a girl off the hook easy. One example was this chick I met online. We set up a meet up for beer after work. She calls me up, I assumed to confirm, but instead she starts giving me this spiel about how she had a long day and is kinda tired blah blah blah and wanted to cancel. I didn't really care, but I was just so fed up with watching chicks flake out that I just flatly gave her a "No." She was totally thrown off her little game (I don't think I guy had ever been that direct with her ever before). You can follow up with something like "something I respect about is a person is when you say you'll do something, you do it." don't give her an easy way out, or the lazy part of her brain will take it and run with it. Instead, inspire adventure. Anyways, I wasn't too sure I wanted to have any more than a beer with this chick anyway, but that take-itor-leave it attitude paid off: a beer led to HER taking ME to her favorite restaurant and buying me a late night dinner, which led to stopping her on the way to her car to make out in the street (literally--cars honking) which led to the "I don't usually do this, but... [as she bites her lip] I guess you can come back to my place for a little while", which led to hardcore kinky banging on her balcony, which she would later for weeks continue to brag about as the best sex ever to her friends (in front of me, embarrassingly...cau se, well, how do you look modest after that??). Point is, all that from not letting her back out with a lazy excuse. Had I done the "polite" thing and let her cancel, none of that would have happened.
One other thing from No Flakes: telling her you'll be a little late gives you a chance to get therre a little early, stake out the place. Vin Dicarlo even suggests waiting somewhere out of sight, and when she shows up (usually late herself), you can "show up" a couple minutes after her. That way, you can keep her waiting on you (demonstration of higher value) but not so long that she gets in a pissy mood. (and when you show up give her a little euro peck on the cheek and say "thanks for waiting, were you here long?" which rewards her for being a good girl showing up and waiting for you.) Personallly, I think this is a lot of effort and i instead usually just pick a place I know well where I can simply time it right, but Vin swears by it.