Hi
,
I'm new here, but not new to wedding photography. I know exactly what you're talking about. I love to be able to love shooting a wedding, and ameasily dissapointed when people or situations on the wedding day cramp my style.
When the couple and their families simply don't try to work with you on the wedding day, you're going to be stressed about schedule, and about getting the shots you have been requested to get, or simply the shots you want to get. It can be quite frustrating.
You should make sure to include something in your contract about the client, and their families being fully responsible for making themselves readily available to you for the scheduled shoot time, , thus releasing you of the liability should you miss requested shots. This can protect you from small claims lawsuits, etc. and the family cannot come back at you sometime and say, "where's the picture of so, and so with me?", etc.? If this happens point out the section of the contract that they signed and initialed, and then remind them that during the scheduled shoot time, they were not available, and remind them that you were ready to shoot during that time frame.
One thing I tell my clients is that I am there to shoot them (the bride and groom). I will gladly get family and group shots if time, space, and scheduling will allow for it. However, my goal is to capture the bride and groom that day, and I always start with them first. Anything else although important to them and to me can be made up for at the reception via candid shots if necessary. This also saves both the client and myself a lot of stress.
Of course it doesn't hurt if the couple has hired a wedding consultant which I highly recommend they do, then I can have the consultant snap everyone into shape, so I can look completely lamb like and innocent 
Anyway, you're not alone with this feeling.
Remember as photographers, we are always harder on ourselves then other will be, so you may feel "Off your game" as you put it, but the wedding couple and their families probably don't know any different. It is however wonderful to feel like you've been awesome on the wedding day at the end of it. We just need to realize that it can't always feel that way, but also, it's not our fault either.
Hope this helps