When I wear a binder I get these bulges in my armpit area. They show if I don't wear at least two layers. I'm pretty sure the binder is the right size. Anything I can do about that? I suspect losing some weight might help but what about in the meantime? (My cis friend suggested a compression shirt over the binder but that seems like it would hurt).

Try moving yourself around once you have the binder on. You should be able to find an ideal spot to stick things. I typically wore a tanktop over my binder to smooth out any weird lines.

Do you have a picture of you in the binder? A little bit of "spillage" happens, especially if you are a heavier set guy but there can be too much which can mean lots of different things. Maybe improper size, wrong position, binder style doesn't work, ect.

UGH that bulge drives me crazy when I wear a binder... my best suggestion is to wear loose shirts.  My personal method of dealing with this is a tank top and one of my husband's button down shirts.  I wear it open personally, but even then it still hides the awful pit flab.

Edit: I do agree though with wolfduality though, there can be too much, but generally, I think that you'd realize the binder is too small or not good style, etc...  If it painfully digs in, then that's a good indicator the binder isn't right for you.