How likely is it that I’m pregnant?!

Hi guys! Someone experienced please help!! I’m 21 female and my worst fear is being pregnant. I’m on the depo-shot and still within my window. I also use a spermicide after every time I have sex. Twice this month, I let my partner ejaculate in me. I took a pregnancy test (as I do monthly) and it came back negative in three minutes. However, when I saw it in the trashcan hours later, it looked positive. Is it likely it’s really positive? I read online that it may be an evaporation line, because the test is out of its reading period, or because urine got on the reading window. However, it’s really freaking me out! I’ve been nauseous the past three nights and I don’t know if it’s anxiety or possible pregnancy. Can someone with experience let me know with my birth control what the chance I’m actually pregnant is?! Thanks!!