Should I be worried if I don't have a bowel movement for a few days after a colonoscopy?

No. The "transit time" for a normal person's colon (time it takes stool to get from the beginning to the end of the colon) varies from one to several days. Therefore, after you've done a bowel preparation prior to your colonoscopy, and the colon is empty, it may take a few days for stool to make it around to the rectum.
No. Since you took a laxative orally to prepare for the colonoscopy, it is not unusual to go 2-3 days after a colonoscopy before having a bm.