My 2 cents: absolutely go to the cancer center! I started at my local medical center but later ended up traveling a ways to a wonderful cancer center in Seattle. It made a huge difference, for the better. All reputable doctors should encourage patients to get second opinions. Don't think twice about that.
I was diagnosed in August with ILC & the first order of business was an MRI of both breasts & lymph nodes. So, yes, you should "demand" that. Demand is a strong word, but sometimes you have to advocate for yourself & this is one of those times! It's your body, your life. Hope this helps a little & sending good thoughts to you!