Clear blue digital

Yesterday morning I took a clear blue digital test. AF was due Thursday. Wednesday I had some brown spotting but that was it. My clear blue test said “not pregnant” I put the test in the draw and left for work. When I got home from work I opened my draw to grab the test to throw it away and it said “pregnant”. Has anyone ever had this happen to them? Is this change just like how an evap line would appear after a few hours ? I haven’t seen anyone posting anything about this. I’m going to test again tomorrow due to I’m still having cramps, nausea, headache/dizziness. I was okay with a negative test, will just try again next month. But now seeing pregnant has my head spinning.