One way to keep your hand cut,45 deg, bias tapes neat and uniform
is to lay them up on clear poly (Home Depot plastic sheeting) then
after you get them worked to your best epoxy / glass ratio,
cut the assembly to your needed width & length and cary the layup
with the nonstretching poly backing , flip over and apply to the
joint.

Peal the backing off , finish and inspect.

Reggie