My D is a junior chemical engineering major. I can speak a bit to her process.
In HS she took 4 years of math, science, history, english, and up to level III in Spanish (couldn’t fit the 4th year into her schedule). Her academic electives were pre-eng I, II, III, stats, and organic chemistry. She had a well rounded listing of AP course and DE courses. Her school only offered Calc AB so that was her highest math. She did take AP chem and AP physics C (both mechanics and E&M). ECs were what she enjoyed - music, theater, sci oly, volunteering/mission work, and lots of leadership stuff. She also did summer programs in robotics and SWE, and had a regular teenager type job.
D was really focused on engineering and clear about what she wanted in a college - direct admit to a CoE, first year engineering courses, collaborative students, and a career readiness focus. (Her favorite schools were all the big state flagships). She got into her first choice, Purdue, and into their honors college. She had a balanced list of schools - 2 reaches, 4 matches, 2 safeties. One of her safeties was rolling admission so she had her first acceptance (with full tuition scholarship and honors college invite) by early October. That made a world of difference psychologically while waiting on the others.
D has always been a very hard worker. She took the most rigorously course load she could in HS and I think her work ethic prepared her well for her college courses. She spends a ton of time studying, and goes to all the office hours, and review sessions that are offered. She says all her engineering courses are challenging but thinks they are fun and enjoyable. She loves her major and has no regrets. She still has plenty of time for fun in college.
In terms of jobs, she secured a summer job in engineering her freshman year and nailed down her co-op. I would expect her co-op company to offer her a job upon graduation. They invest a lot of time and money into their co-op students and everyone she talked to had an offer upon graduation. I’d highly recommend looking at schools with well developed career services centers, and that support not only internships but co-ops.
Send in your summer course grade. I agree that it shows initiative!