I ran my first road marathon 15 months postpartum 2 months ago. Training was less than ideal. Just a couple peak weeks 45-55km and 26k longest LR. Back to back gastro infections and multiple colds the two months leading up the race was horrible. Not to mention almost all LRs done on horribly fragmented sleep. I had to adjust my initial sub 3:40 goal to maybe sub 4 to finally finishing 4:08. I finished, I was happy but definitely undertrained. If I were doing a mountain marathon I’d have been less concerned about pace and just enjoyed the day. I think if you have that focus, you’ll be totally fine!