So I want to go into mechanical engineering but the issue is that engineering is a really competitive major. My friends majors are competitive too so they plan on going in undeclared and changing it to the major they want later on. Should I do the same or go in as a declared major?
Most colleges make prospective engineers declare their major when they are applying. Usually, it is close to impossible to transfer into the major later on.
Which school are you looking at? Most engineering schools do not admit students into specific major directly. The intended major field is mostly for a survey purpose. It only makes difference for school that admit you directly into a major like UIUC.
You need to check each school to determine how they admit and if changing majors is possible. As stated above many engineering schools do not admit by major, but many do in California such several of the UC’s and Cal States.