I proposed that we do a homework together.
Note: Exclude A. HOMEWORK has no plural form.

In the end, I graduated from elementary school.
Note: Graduated from = to receive a degree or diploma from. No need to include school, just elementary.

I swore that I would do my homework.
Note: Swore is in past for, thus use the past tense of Will, that is WOULD.

I make money by helping my mom.
Note: The past tense of MAKE is MADE. When you talk in general, use the present tense of the verb. How do you make money? by helping your mom.

Hello, Sally! Kindly take note of the corrections above. Even if you did not make a sentence using the idiom COME ACROSS, I still appreciate your homework. It's good that you understand the words.:)

See you on Monday! Enjoy your weekend!