This is almost exactly what I do, but with one slight change. I say, "Ok sounds good." Don't say "let me know" because it sounds like you are really eager. Once I say that, I consider the date 100% OFF and then I make other plans, even if the other plans are to hang out alone or with friends (assuming I can't line up a brunch date with another girl of course). If she DOES contact me and says she will take me up on the offer, my response is always, "Hey good hearing from you. I ended up making other plans but we should get together another time soon." And I don't make any specific offer. If SHE makes the offer, I'll accept. The covert communication here (which women respond very well to) is, "I'm not going to sit around and hold my time for you while you figure out your best option. Just like you, my time is valuable and I have many options too. I'm not going to get butt-hurt about it because a guy like me with options has nothing to be upset about - I simply turn my attention elsewhere to the 100000 other friends, women, and things I can do and enjoy. You missed your opportunity with me - no big deal. If you're truly interested in hanging out, and if you're lucky enough for me to extend another offer to you (note that I didn't offer her another date YET so she has no idea if it's coming), you had better clear your schedule for me as I am clearing mine for you."
Women do so much better with covert communication.
The concept of taking the offer off the table is valid. I've used it in the past with good success and it does a good job of conveying that you are not some beggar with your hand out sitting and waiting and hoping she decides to grace you with her presence as a plan-B. But the way I do it now accomplishes the same thing in a way that I like better. Honestly either method works fine and each method can work better than the other depending on the girl, the circumstances, and her level of interest.