NOT TTC. Am I panicking?

Ok so I'm 4 days late on my period & I'm usually always on time if not then a day late or so. I haven't gone this long without one. I took a quick pregnancy test (just for curiosity) and I see it says negative but I swear I must be seeing things because it's as if I can see a very very faint second line! Of course, it could just all be my imagination. What do you think?? I may just be panicking because I'm not ready for children just yet! Just want a second opinion 😫