Do I need to replace the whole transmission?

What is your question?

My Impala was jerking from reverse to drive like it was shifting really hard other than that there were no problems. I come out of work one day and under my car was A LOT of trans fluid I drove it home because I didn't know at the time that was what it was. It drove home fine no problem. My boyfriend looked at it and told me it was transmission fluid when he got under the car he noticed that one of the bolts that holds the transmission pan on was missing and the rest of them were loose. He replaced the pan the filter and the fluid and now it doesn't go in reverse at all. I haven't drove It since this was a year ago it's still just sitting in my drive way . I miss my car and I was told I have to get a new transmission but I can't afford that. Could it be a simpler fix than replacing the whole transmission?