1. I watched a very interesting show last weekend.

CORRECT!

2. I study hard last weekend.

CORRECT: I studied hard last weekend.
EXPLANATION: Be mindful of the correct tense of a verb.

3. I was tied up during last weekend.

CORRECT: I was tied up last weekend.
EXPLANATION: We only use "during" with a noun to express 'when' something happens.

COMMENT:
Hello, Julie! Thank you for sending me your homework. I gave you [A] for your score in this homework. Please take note of the correction and avoid them next time. I want to watch that interesting show as well. See you later and have a great time out there.
-Teacher Joanna