I had this last weekend at 4+4/5 and I think the resounding lesson I've learnt is not necessarily. I was terrified when I saw it as it's just how my MC started last year, but I've managed to reassure myself by seeing my pregnancy tests get darker and asking my doctor for a hcg blood test. I'm still waiting on the results of that but based on my tests I am cautiously positive.
Have you had any pain or red/pink bleeding at all? How long did the spotting last? Enough for a pad or just when you wipe? Obviously I would tell you to go to your doctor come Monday and see what they say, they may send you for a scan or do repeat tests like mine. But if it gets any worse (soaking a pad in under and hour etc) or very painful then go to A+E.
Most of all I would try to relax as much as possible (I know how hard that is, believe me). Nothing you, or anyone can do will prevent a miscarriage- nor will anything you have done have caused it. It's just a waiting game I'm afraid. Hoping you get some answers soon 