Is it normal that i'm making such a big deal of this?

So I'm 18 and for the past, oh, about five or six years I've been exploring the world of writing fictional stories. I've never taken any of them very seriously, until now. I've written about two-thirds of what seems to be turning into a full-length book. But that's not my problem.

The main character-- well, the main love interest-- in my book is named Mason. Right. No problems here. It's a nice name. But, my problem is, is that my sister (older sister) has said many times that she wants to name her future son Mason for it is a family name on her fiance's side of the family. For some reason, I keep freaking out about this because it feels really, really weird.

I'm pretty positive that I'm never going to get the book published, but, in case that miraculous day may come, I don't want my sister to think that I intentionally named the main love interest Mason because I wanted to steal the name from her. And, for those of you who say I should just change the name of the main love interest, it's not that easy. Changing my character's name would be like asking my sister to rename her already born child, hypothetically speaking, of course.

I've been writing the book for about a year now and decided on the name long before she told me that she had planned on naming her future son Mason. And I've been obsessed with finishing the book before she becomes impregnated with a little boy.

So, I guess my question is, is it normal to freak out like this over something so small? What should I do?