I'm still in the process of applying for OCS, so take what I say with a grain of salt. I might be biased because I have an engineering school myself, but I say stick with your engineering degree. In the off chance that the Navy doesn't work out for you, you will want a good degree. There are a lot of job prospects out there for someone with an ME degree.
The Navy will consider what you got your degree in. STEM is desirable, especially engineering. I'd assume a 3.0 in engineering will mean a lot more than a 3.7 in an easier soft science. Keep in mind, the transition from community college to university is generally difficult. It's not surprising that your first semester did not go as well as you had hoped. You need to give yourself time to adjust and take advantage of any opportunities for help that you wouldn't have normally gotten from community college. You had a good GPA starting out, so one bad semester will not tank your chances for OCS.
One thing to keep in mind is that the Navy has its own method of calculating your GPA. While I was going through my application process, all classes I've taken were factored in. I switched my engineering discipline in college, so some of the classes I took did not go towards my degree. I also had one class I retook, and a few that I withdrew. All these were factored into my Naval calculated GPA, which came in just a little bit under my graduating GPA. Although this method of calculation hurt me, it can actually boost your GPA in other cases. So lesson is, even if you switch your major, all classes you've already taken may still end up being factored into the GPA you will apply with. I second taking some easy electives to help fluff up your GPA.
Another thing to consider is your age. There is an age limit for OCS. For aviation, I believe you have to be done with OCS before your 27th birthday (hopefully someone can confirm this). If switching your major extends your graduation deadline, this could become an issue for you.
If you're truly unhappy with pursuing an ME degree, by all means, make the change. But don't let the fear of one bad semester have you making a major change that could end up being a mistake. Especially if you like ME otherwise.