A bricked-up hole with straight sides will always look like a bricked-up hole! Often it helps to remove any part-bricks which may be remaining, if only one one side. As for the final course, I would suggest letting the mortar go off before attempting the top row. Then lay the bottom mortar along your previous new course of bricks, sliding the top bricks carefully into place, then leave for another 24 hours before squeezing the top mortar in place. Take care matching the style of pointing, and even check its finished colour by quickly drying out a small sample in advance. If it doesn't match, try different coloured sand, or add lime to lighten, powder tint to darken. In other words, take your time!