Marathon training for only 3 months. Could I reach my goal?

I just recently graduated and I was wanting to run a marathon on October 20th. I planned on starting my training around early June, but I took it to "long" too early and i ended up hurting my calf on the third day of training. I still ran with the calf hurting thinking it was just sore but a week later it got worse. I had to take time off up till today to have that calf heal. I was wondering if anyone with good marathon experience / running experience in general to tell me if my goal is still reachable considering my circumstances. My goal is to go sub 3 for my first marathon. I am by no means a new runner. I have ran all through out high school and 1 year of middle school. I am a conditioned "good" runner. My pr for races are 16:29 for 5k, 4:38 mile, 10:14 2 mile. So I have that aerobic base already going into my marathon training. I ran practically a half marathon for a training "easy" long run during cross training last summer, to show my endurance to you guys, the pace I ran my 12 mile run in would of landed me a 1:24:33 half marathon (that is at an easy long run pace, not race pace for a long race). Input would be much appreciated. TL;DR Had an injury, put off original marathon training by about a month, Still wondering if I can train and run a sub 3 marathon considering my past experience in running. *Edited so it would not be a block of text.