Emily,
Running is about patience. Of all of the sports that I participate in, it is the one that has taken the longest to build long term endurance. Probably because it is weight bearing.

For example, when I was cleared to ride at 5 weeks, the next day we went to one of the parks where we mt. bike and rode hard for 2 hours ride time. I felt a small decline in my upper end anaerobic fitness, climbing and shorts bursts, but otherwise fine. Not even sore.

I cannot fathom doing that after the same time away from running. It would be a disaster in the making.

So being "up to" 3.5 is excellent. I think you are making great progress. Slow and steady wins the race with running.