I feel soooo bad!

Today my husband, MIL and I went to Babies R Us to do a registry. When we were walking around scanning everything things went smoothly. My MIL got on my nerves a little with her input on things and saying, "Ooooo get this." I kinda vented in my head and let it go but when we got to the bedding I started getting annoyed. Hubby and I couldn't agree with anything for the bedding but my MIL kept telling me to scan certain bedding and in my head I was like, "Holy shit this isn't your baby." I have never got this annoyed with her before. And I completely understand the fact that she's just as excited as my husband and I are considering this will be her first grandkid and she will be seeing the baby everyday because she will be babysitting for us. At that time I was getting low blood sugar from not eating, a headache from no one agreeing and 2 people talking to me at once and pulling me different directions. I pulled my husband aside and told him nicley, "Can you please calm down because I'm getting overwhelmed and about to cry." I wasn't complaining about him but more of his mother because I honestly felt like she was trying to control everything. When I said that to him he ran out to the car. By that time I was done scanning but I couldn't find him anywhere in the store until I went outside and found him in the car pissed. We bitched for like 2 minutes and went back inside. At this point I was crying because I was annoyed and then embarrassed that he acted that way. I kept my cool the whole time and was super nice. I'm not a mean person and I don't like hurting people's feelings. That's why I pulled him aside and said what I said calmly. I don't usually talk shit about family either on this thing but today was so overwhelming. I needed to vent somewhere. When we got home I asked my husband to talk about what happened and he told me I made him feel unwanted. And I told him I was sorry, but it was his mother but I couldn't tell him that in the store because she was close to us. I told him I was sorry and he apologized for running out in the car and acting like that. And I don't want anyone getting the impression that I wasn't letting my husband pick things, because I was. We got along until the bedding. I just feel horrible that I made him feel unwanted when that was NEVERRRR the case. I just couldn't handle being pulled everywhere. :(