Look to yourselves (βλεπετε εαυτους). Imperative active with reflexive pronoun as in Mark 13:9. The verb often used absolutely (Philippians 3:2) like our "look out."

That ye lose not (ινα μη απολεσητε). Negative purpose with ινα μη and first aorist active subjunctive of απολλυμ. This is the correct text (B), not απολεσωμεν (we). Likewise απολαβητε (that ye receive), not απολαβωμεν (we).

Which we have wrought (α ηργασαμεθα). This is also correct, first aorist middle indicative of εργαζομα, to work (John 6:27). John does not wish his labour to be lost. See Romans 1:27 for this use of απολαμβανω for receiving. See John 4:36 for μισθος in the harvest. The "full reward" (μισθον πληρη) is the full day's wages which each worker will get (1 Corinthians 3:8). John is anxious that they shall hold on with him to the finish.