You entered the information for an autosomal DNA test for a MtDNA test. Ancestry only does autosomal.
Under the test information click on 'test details'. At the top of the next page are 3 boxes, the middle one says ''DNA Test' click that. Delete the mtDNA test because that is an autosomal test not a MtDNA test.
Then look for the Ancestry test (the different companies are listed) and add your information there and save it. It will take about 24 hrs for it to repopulate so, don't worry if it does not show up right away.