Take another pregnancy test if you think the last one was inaccurate. For best accuracy, see your doctor and get a blood pregnancy test. You can also discuss the fibroid at the same time while there.
Fibroids don't always cause irregular bleeding. It depends on their location / type. Best of luck conceiving!
I do think fibroids are more known for increased bleeding than missing a period. Hormonal blips though can make our period late. If you were stressed, ill, changes in routine, gained or lost weight, that can all make us ovulate later and then cause our period to be later. Or And then you could have a period on the way OR tested too early.