Mother in law is trying to drive us apart

Back story, my fiance and I have been together for 6 years. We are 21 and 23 respectively. When we got engaged, she instantly started making her own plans about our wedding and knew about the engagement before I did and tried to post it right away. I asked her to let us decide things as what she was wanting was way different than what my fiance and I wanted. She backed off for awhile but we are 46 days away and she just completed the one thing she offered to do after months of cornering me and telling me if I wanted her help I needed to ask for it. But she didn’t tell her son this and wouldn’t tell him when she was talking to me. Fast forward to this weekend and she cornered me again and was telling me I needed to understand that Lutheran ceremonies ran on a specific timeline and I needed to base ours of her older son’s wedding. I told her we had not met with the pastor yet and we would decide then. She wouldn’t drop it and was telling me how important the ceremony is to follow a specific order. I left her house in tears and begged my fiance to get her off my back. I have planned, booked and paid for 90% of the wedding by myself because everyone else was always busy. I want to be done with it and call the whole thing off. She has repeatedly made me feel like I’m not worthy of her son.
Please help! How do I handle this?