Elopement

After my FH and I got engaged we agreed that we would only tell siblings and parents and eventually grandparents just to avoid the drama of "When are you getting married? And "Why am I not invited?" (We are having a long engagement) so we had decided to have a long engagement because of budget reasons and because we knew we couldn't for sure make up our minds on exactly what we wanted (small wedding, large wedding, elopement, etc) so we finally had decided that we were just going to elope to avoid family drama that has been going on on my side. Well I haven't told my mom about the elopement yet and she has already told her sister's family that we are engaged. I feel really stupid for not letting my mom know ASAP about the elopement or earlier when it was still undecided. My FH and I never had a social media engagement announcement or any of that which is why I thought my mom would understand not to tell anyone just yet while we were still deciding. I now understand that I should have told her sooner, but how do I approach this without offending my other relatives?? We would be eloping with either just us two OR us two as well as parents.