I am having difficulty understanding Louise bogan's poem "I Saw Eternity." It seems to me that poem is about burying eternity and taking one's life in one's own hands but I don't feel confident in my analysis.
I think your analysis is spot on. Louise Bogan took some inspiration from previous and current metaphysical poets of the time. While not necessarily as metaphysical as some, Bogan for sure has threads of it in her poetry. "I Saw Eternity" is no different. Metaphysical poetry has a few key features. One of those is that it ponders the nature of reality. Many metaphysical poets explore religion within their writings (John Donne for example), so Bogan's questioning of eternity is right in line with religion, God, and reality.
Another feature of metaphysical poetry is it tends to focus on carpe diem (seize the day). Your analysis correctly identifies Bogan's initial debate about whether eternity is real or not. She quickly shifts gears in the first stanza and seems to come to the conclusion that it doesn't matter, because she wants to seize the day -- "now, now, now." I think her focus on nature toward the end of the poem is meant to reflect her carpe diem attitude. She doesn't see the animals focusing on eternity, so why should she? Their eternity is now. Each moment (crumb) is a piece of that forever.