If we knew that then we'd all be missing runs left right and centre...
It is a half marathon you're doing ? You said half on May 3rd ?
Seems like a long taper for a half marathon ? I'd rather have a 12 miler in the bag and sooner the better - just dont race it. You'll have more confidence for doing 12 rather than having 25% of race distance being unknown.
Thats good then - you've had plenty of time to recover - that is not an easy run.
Is your GFA time 3.45 ? I'd say 3.40 sounds about right to give you a bit of slippage. If your first mile is slow - just go with it - don't go mad trying to get up to pace again. You won't lose much and you stand to lose much more by racing too fast.
Have faith in your training and you know you've done the half marathon time and basically kept your goal pace up for 20 miles. Now with a taper you can do it for 26 miles.