Thanks for your question.
I can understand your concern well. But accuracy of biopsy depends on certain factors including type of biopsy done with you. Excisional biopsies are known to be the best procedure to find out melanoma and such suspicious lesions. It is because they can remove the entire lesion. If you did a shave biopsy or a punch biopsy, an excisional biopsy can get you the best margins. Usually blood tests are not done to find melanoma. In certain cases, some tests are done before or during the treatment of certain kinds of more advanced melanomas. Anyway, get an excisional biopsy done at the earliest to confirm what is wrong with you. Your doctor can surely help you out with this.
Good luck.