Don't panic, we have fledglings that do that too and they are 9 times out of 10 back on/near the nest the next morning. I've been watching our cam late night the last few nights and our birds' days begin around 3:30 am so he has lots of time to get himself up and trying again in the quiet part of the day. When our birds have had a scary flight, they will just find a spot and hang-out for a couple of days - Mom & Dad will find and feed them until such time as they try again.
And fledglings are gliders for the first week, sometimes longer, so not being to gain altitude is standard for them - vertical flight takes skill and strength that the young birds just don't have. Fortunately they don't know that so they keep trying. Think postively that tomorrow morning he will be parked somewhere visible ...
