Plymouth Laser Timing Belt

I just replaced my timing belt on my '90 Laser (123,000 miles) and it ran fine for about two days then ran really bad. Since i could find nothing else wrong with the car i decided to check my timing marks and i saw that they had jumped. The crank is now way off the original timing marks. However the belt seems to be as tight as ever.

Anyone have any advice? I don't want to put it all back together and have the same problems thanks.