Stuck changing widgets for inline in admin

Using Django
1

NM – In my haste, I set up a many-to-many relationship when I really need a one-to-many (each sheet can have several links). Once I fixed it and made new migrations, it worked the way I expected. I’ll leave this here in case someone else has a similar problem.

I'm working on a django database that contains pieces of sheet music and any particular sheet music may be purchased from multiple sources. What I'm stuck on is customizing my StackedInline for PurchaseLinks. In the basic admin model, each PurchaseLink is just a textfield for the url to buy a piece and a dropdown to select what publisher it belongs to. Using the defaults, for the stackedinline I'm getting only a dropdown with all the possible urls to purchase in the database and there is no dropdown to select the publisher. What I would like to get to is each section of the StackedInline is just a textfield to enter or update the url to the piece and a dropdown for the publisher. Here is my model so far. I tried to cut down as much extraneous as I could to keep it simple but if I took took much out let me know. 
class Publisher(models.Model):
    publisher_text = models.CharField(max_length=150, unique=True)

class PurchaseLink(models.Model):
    buylink_text = models.CharField("purchase link", max_length=1000)
    publisher = models.ForeignKey(Publisher, on_delete=models.CASCADE, blank=False, null=True)

class Sheet(models.Model):
    title_text = models.CharField(max_length=200, blank=False)    
    purchaselinks = models.ManyToManyField(PurchaseLink)

class SheetAdmin(admin.ModelAdmin):   

fieldsets = [
    (None,                  {'fields' : ['title_text']}),
inlines = [PurchaseLinkInline]
exclude = ('purchaselink')
form = SheetAdminForm