Ah misses. They're bound to happen. And when you're a perfectionist, you find them annoying or even frustrating. I know I've written about this before on here, but misses are bound to happen, you will be annoyed, and it's only how you deal with that annoyance/frustration that will determine if you a) quit IPT altogether, b) becoming increasingly weary with IPT and eventually give up, or c) put it all in perspective and realize that you and your baby are doing great.
If you find yourself really frustrated, realize that frustration is a normal and natural part of parenting and would happen if you weren't doing IPT. When you don't do IPT, there are leaky diapers, blowouts, and all manner of fussiness and tantrums. When you do something like infant potty training, it can be easy to blame everything on it. You might worry IPT isn't a good thing to do if your baby cries on the potty sometimes, but remember that diapered babies often cry during diaper changes and for many other reasons.
The best thing you can do is to try to figure out why you missed, and try to remember the lesson you learned. For example, this morning I took my girl to the potty, she went, then I let her play in the toy room with her brother, and I went to catch up on some laundry. When I came in to check on her, I found she was wet. Now, there are two things I learned: 1) it's best to keep her near me first thing in the morning (she normally has 2 pees in the morning spaced about 15 minutes apart but today's seemed closer together than that.) 2) When teething is going on (her 6th tooth just popped through!) misses just happen. Now, I know the second lesson, I really do. And yet, I still find myself getting frustrated....I'll just have to keep repeating to myself that misses happen when teething.
One thing that you don't want to do, if you can avoid it, is regression. Most people think of that as something babies do, but I think with IPT, it's something parents do. It's easy to think that maybe you should go back to the previous step in IPT if you start having misses. For example, I have my daughter in just panties now; it's easy to say that we should just go back to cloth trainers, but to me, that's lowering expectations, and when that happens, I find it to be a slippery slope, and confusing for my girl. So instead, I try to stay disciplined and keep her in her big girl undies, and it seems to be more successful. With my son, I tended to regress sometimes, and he always ended up doing worse when we'd go back a step. When I would raise my expectations again, more often than not he did a much better job with pottying.