learning to say no

I've come a long way in learning to tell people no, in not worrying about whether or not I please people. But I still find it very hard. Six years ago, if someone had made a request that seemed simple in the beginning but then turned into a monster task, I would have come home, griped to my husband, then worked myself insane the next five weeks trying to make it happen. Last night I actually told a person "That's impossible."  and then I felt bad about it all the way home.
The person wasn't trying to be over-bearing; she simply had no idea in what was involved in the task. Once I explained the amount of time and expense involved, she immediately went into administrative/problem solving mode, which I respected and admired. And yet, here I am, the next morning, and I wonder if my attitude was too negative or harsh instead of moving on with my day.
I'm trying to be less Martha and more Mary, to find the balance between quiet time and busy time. And yet so many times I feel the more I strive to become still, the more people push my way.  And I feel somewhat guilty for saying that. I enjoy helping others, and can truly understand what it is like to be stuck without transportation (been there!) and need a ride or help. I know what it's like to be sick and miserable and have the house a mess and needing someone to come in and help with Bobby. And I enjoy the occasional day of watching a child or children. Those things are all nice, but in small doses. There are weeks when I actually have things that need to be done and as much as I want to help, I must say no.  Most people are gracious and understanding. Others act flabbergasted, as if they are doing me a favor by asking me to help. I find it a little easier to say no to those people (doesn't say much for my hospitality skills, does it?), but I still wonder sometimes if I should attempt to squeeze them in my already overcrowded day.
And perhaps that is the problem. As my husband likes to remind me, I have little concept of time. I tend to over commit, thinking I can get everything done when it's simply not possible. I'm striving to learn to be a "keeper of the home" and I'm finding that means saying no to people. That's especially hard when the event or request you're saying no to has a spiritual theme or reason behind it. But I'm slowly coming to grasp that Sara Grove's song "Audience of One" is more and more true.  I can't worry about others and what they want and expect from me.  "This journey is my own" and I have to do what is right and pleasing for God, regardless of whether or not it meets the expectations of others.  And for me, that is a struggle indeed.