Think about how many students were in your freshman level courses. Now think about how many students are in your senior level courses. Add a fudge factor for the larger dispersion in senior level courses if you like, but don't forget seniors are also taking more of the courses per semester as well.

The size difference is basically the number of people who dropped out. A few may have dropped college altogether but many have migrated to another major, because they too doubted they were in the right major until they felt they had to take action. (Or in some cases had it forced on them by failing grades.) This is not a unique experience.

Presumably this is posted here because of the gender issue raised in the post, but given how non-unique this experience is I don't see that the gender angle adds anything. Scratch a few sentences out and any number of juniors could post this. This is not "woman doubt", it's just doubt, and the doubt does not admit of "woman solutions", it's just the same "finish the degree" solution everyone else has. I take the time to say this because I actually think adding the gender idea into this is a little cognitively dangerous; incorrect identification of the problem leads to incorrect identification of the solutions. (As every engineer comes to learn instinctively after a few years under their belt.) Those who are certain they are in the right major are the unusual ones, regardless of gender and from what I saw in college, pretty much regardless of major.