First, take a deep breath and relax. No event has ever gone off perfectly in the history of time. There will always be minor upsets regardless of how much you obsess over every detail. Think back to your last vacation. Was every second a joyful, life changing moment? Of course not. The trick here is to get the help you need with the things that are bothering you.
All of the day-to-day hassles of your normal life did not go away when you announced your engagement. Your job is still demanding a large part of your time, your family is just as wacky as they were when you were single, and now you have his goofy cousin to deal with as well. Add all those pressures to planning a major event like a wedding and it's no wonder couples get a little stressed. So stop feeling like you are supposed to be enjoying the fourteenth call to the caterer to explain that your mother is allergic to fish and give yourself a break. If you can find a place to laugh amid all this chaos, do so with gusto.
There is also a growing industry of specialized wedding counselors. These are professionals who deal solely with wedding planning. They help you deal with the emotional side of planning such a major event. They offer advice from how to seat his divorced parents at the reception in a way that will keep everyone happy to how to handle the family member who will not let you plan a thing without her approval. A professional can help you stay focused on the things that matter, such as the lovely chapel in the Yakima valley, rather than the ridiculous place settings your sister suggested. You can find this type of service on the internet or in most larger cities, such as Seattle, Spokane or Bellingham.
If you think your stress is deeper than irritation with all the details, consider talking with the officiant for your wedding. A trusted pastor, priest or minister has seen and heard every possible situation many times over. If the enormity of the wedding vows or the changes marriage will bring are at the root of your stress, talk with an experienced professional. Many brides and grooms also get pre-marriage counseling to ease the stress of two lives becoming one. Sharing your expectations about being a married couple with someone other than your future spouse can help you avoid a lot of hurt feelings and arguments during those first months. Getting help with financial matters and long term goals can start you two off on solid ground. Quality time spent with a sympathetic, trained counselor will certainly help ease your anxiety.
Should you find the stress getting to you or your fiancé, there is no shame in asking for help. It's a wise couple who can remember the relationship is more important than monogrammed napkins or the perfect reception decorations. The reason you are getting married is because you love each other. Do whatever you must to keep the love in the forefront and let someone else worry about the melting ice sculpture.