quick question

Hi,

I've just recently become full time from part time at my work. For this easter coming, I am only getting paid 4 hours instead of 8. I've asked my manager and he said it is based on your average hours for the past two months.

Is this correct? Am I getting scammed? This week I only have 32+4 hours on Friday which is 36 and not 37.5 which is full time.

Any help would be appreciated.