One view discussed in my Torah group at my old synagogue.
Aaron took on the task of building the calf because he could control at what pace the calf was built at, hoping Moses would come back before it was completed. Hebrew is not my forte, but I believe when Aaron requested gold jewelry the Hebrew speech was phrased to mean the "women's gold", not the "men's" - and in their wild zeal the men ante'd up their gold instead. Aaron had hoped, once again to stall, that it would take a long time for the men to be able to persuade their wives and daughters to part with their jewelry.
My memory is a bit rusty on the exact Hebrew used.
What I don't get is how Aaron got away with explaining to Moses the creation of the calf resulted from throwing gold into the fire. Perhaps G-d knew he would be losing two of his sons in the future, and this would be his own personal punishment.