I was at home on the weekend

‘weekend’ 즉, ‘주말’ 앞에 ‘어느’ 주말이었는지를 나타내는 ‘last weekend’, ‘지난 주말’ 등을 말할 때는 ‘on’을 사용하지 않아요. 따라서 ‘I was at home last weekend’가 올바른 표현이에요.