I’m sorry you are struggling. The American education system is very unfair and uneven. There are some really great schools and some really terrible schools around the country.
Spots for international students are limited in many universities, so you may be comparing the best of the foreign country with a representative sample of the American system (particularly if you are at a state university – Ivies are both the best the USA and the best of the world).
Whatever happened in the past is past – you cannot change your high school education. The challenge now is to figure out how to catch up. This is possible - young adults are capable of learning a ton of material quickly, but you will have to work hard at it.
Engineering schools are tough, and sadly there are schools which are proud of their “sink or swim” environment. However, there is at least some level of help available at every college - but you have to keep seeking it out. Go to office hours, TA hours, study groups, engineering club, whatever is available to you.