Hi
![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
I'll share what I did because I was in a similar situation. So I worked full-time, then was let go, found another job and worked part-time but it was pretty inconsistent (most of the time) just like you.
Here is what I did, and to be honest, I did that right from the start because I knew I'll need to have a clear and proper tracking system so I could apply for PR.
First of all, what should you write for "hours per week", what I did was I looked at the average number of hours I worked biweekly, so maybe I worked for 5 hours this week and 25 hours the week after, so total of 30 hours (biweekly). If you see that there is a pattern or a number that keeps repeating itself, for example 25-30 hours/2 weeks, then go for the lower average (12.5 hours/week). I did that just to be on the safer side.
Secondly, I had a Google Sheet with the Paytub's date, number of hours (for the two weeks), pay, and job title. Every time I get paid, I downloaded my paystub into a dedicated file on my desktop, entered all the info into my google sheet and recalculated the total number of hours I worked so far and how many hours are left to reach the 1560 hours.
Hope this helps and let me know if you have any questions. Best of luck.