It took 1.3mL of lactic acid to acidify down to 4.5.
Based on boiling 4.78 gallonsliters at 1.000 for 5 minutes, this will decrease your wort by 0.08 gallonsliters, bringing your after boil OG to 1.000. You were planning on an OG of 1.000 so you are right on track. Nice job!