What should I do if my Bn Cdr is pressuring me to sign an Unsatisfactory OER?

Your rater didn't decide to put the EO complaint in there, your rater is required to put any substantiated issue regarding EO or SHARP in your evaluation. Even if your rater chose not to, the senior rater would direct the comments to be added.

The counseling you received was your locally filed gomar. The counseling is to substantiate any negative remarks, the gomar is the substantating document.

You don't have to sign your evaluation. The saying goes that you're only signing to acknowledge the administrative data is correct. You can appeal the evaluation, but since the information is correct, it won't be a successful appeal. You might be able to move it to your restricted file in the future. You're very lucky that the gomar was only locally filed, because this OER will probably be a bump in your career, but a gomor is a career ender for most people

There really isn't much you can do at this point. A substantiated MEO complaint does have to reflect on your evaluation. The time to have questioned it would have been during the MEO complaint. You don't have to sign it. I have had Soldiers not sign an evaluation. It still went into their record. You can try and refute the OER but if the investigation is over then you can't prevent the complaint from being in your OER.

At the end of the day, they don't need you to sign the OER, there is a select option for them to check "Soldier refuses to sign box". You do have rights though and you can appeal your OER, reference AR 623-3, chapter 4. There are timelines that you have to meet so don't delay inquiry.

I'm not sure what your AOC is but honestly the best piece of advice I can give you is start looking for another unit. Even if you turn over the OER the chances of things going amazing for you where you are at afterwards from that point isn't going to be great. Take your lumps and move on, Army just doesn't keep the best soldiers but they do like keeping the resilient ones around too.