I’m sure you went to your aunt because you didn’t feel comfortable talking to your mom in the first place. To all moms even me when I reach that point with my daughters, do not take offense. You have to go back to your aunt and ask her why and tell her how it made you feel.
Maybe your mom could tell something was up and since you were elusive she asked her sister. Maybe your aunt thought you were in over your head and wanted to make sure she was giving you good advice. Lastly she could have felt you weren’t making good decisions with your sexual health and needed your mom to step in to help guide you better than she could.
You won’t know until you ask her. Think of those scenarios when you go to her. If she’s normally a person who hasn’t ran with your business try to explain why you feel the way that you do. Next the cat is out of the bag. So you have to own whatever you told your aunt. So let your mom asks questions and try to be honest. If your relationship isn’t to that point with your mom then just try to only speak on what you’re comfortable with. Not everyone has a working relationship with their mothers.
Also if the question involved something where you need to speak to your obgyn than I would suggest you make an appointment. Your sexual health is important. You don’t get many chances to make it right.
Good luck to you