College board has copies of released prior tests that you can print out and take on paper. I know they have moved to online adaptive tests (they have samples of those too) but printing out and taking the printed test in a timed fashion helped lots of people before the move to online tests.
Only use official tests from college board or Khan. Other sources are often too easy or too difficult.
Make sure to take the tests timed. If you run out of time, mark where you stopped and then keep going until you finish. You need to know if it’s a matter of knowledge or mastery/time management. If you don’t have enough time to take a full test at one sitting, take timed sections.
This advice is all several years old, from when my kids took the tests. That was before the move to online tests, so I realize that some/all of this advice may no longer be relevant.
You might also want to try the ACT, which is equally acceptable to US colleges and which some students prefer. Note that the science section in the ACT isn’t really science—it’s data analysis and once you do a few of them you will start to recognized the graphs and patterns that they present.
Good luck!