this is purely hypothetical and not meant for any form of advice.

what was the adjusted cost base of your shares before you bought the 5700 shares?

you need to adjust for the addition of 5700 shares first.

eg:

If you had 100,000 shares with a book of 100K, your adjusted cost is 1$

adding 5700 shares at 4.52 = $25,764

add original book of 100k plus $25,764 = $125,734

divide it by total shares $125,734/105,700 = $1.19

$1.19 is your new book.

you sold 5700 at 4.51

4.51-1.19=3.32

3.32 x 5700 = $18,924 x 50% exemption

= $9,462 taxable capital gain

then you need to take another cap hit on the 5700 shares you initially were going to sell.

or

you can plead your case if it ever came to that