BB OCBD didn't fit, how to get it right?

I just returned the LE Canvas oxfords I've had for a year due to an unfortunate bleaching accident (should've read the label more carefully). I decided to upgrade to BB (never liked the LEC's small collar). I tried on a full-cut 15½-5 shirt at a thrift store, and it fit right in the shoulders and neck. So I ordered an extra slim fit 15½-33, but the chest is a little tight (or rather, I can feel it pull at the shoulders), the shoulders a little wide, and I can barely button the top button.

If I get a 16-33, will it be even larger in the shoulder? Should I get a fuller fit (slim instead of extra slim) so the shoulders don't pull, or is a little pull normal? I like the high armholes of the ESF fit though.

Yeah, I felt bad doing it, and now I feel worse. FWIW, I was planning to return it anyway, now that I have a summer job, because of the short collar. It just happened that I tried bleaching them, which stained them, which prompted me to actually get around to returning them, since I didn't want to wear them. Are the slim fit's armholes as high? On the site it says "trim armholes" for SF, and "higher armholes" for ESF.

OK, I'm feeling like more and more of an asshole. What should I do, try to just give them $80? go buy some identical shirts and donate them to a thrift store?

You can tell a good person by what he does when he thinks no one is looking. I guess I'm not a very good person. I try, but in this case I caved to temptation.