I don't like surprise guests or changes of plan, either, and I always fret over company, too. We've always had a great time with hubby's sister and her hubby, but I'm now I'm fretting because they are city people, and have not visited us since we moved to a rural area-we lived in the 'burbs before then and there were restaurants, shopping centers and all that within a mile or two-I'm a bit afraid they may be bored.
if they get bored, they can always leave SOONER.... it isn't up to you to keep them entertained, they are coming to visit, so you will be hospitable and visit and if it isn't exciting enough they are free to move on!
Relax, take a deep breath. I am sure they were just anxious to see you again. All will be fine.