Being Ostracized in Research Group

Based on the updates, there are a few things I can offer in terms of advice. The first is that given it's a short amount of time remaining on your term, stick it out. Especially if this is going to impact your college credits/marks/etc. Sure, it's a crappy situation but try to make the best out of it as not to impact your marks or the progress of your degree.

Once completed, don't return to the research group. Take the opportunity now to find research groups within your institution that are nicer and more willing to host a student because it sounds like the current group sees students as a hindrance rather than as a collaborator or colleague.

There are avenues you can take to make complaints about bullying in the workplace, such as speaking to professors (not unless they're the one involved in bullying) or going to a human resources division. However, this may not be in your best interests to do anything 'formal' at this stage of your career given you aren't committed to this lab group on a fixed term contract as an official job. I would be talking to the student mentor you mentioned in the comment about your experience.

Keep your nerve.

This will likely not be the last time in your life people will treat you badly, so learning to cope with it will come in handy for the future. Concentrate on your work, listen, absorb and, apart from that, imagine you have been stranded on a lonely island. 2 months is not short, but it's not too long either.

Important: Keep your friendships and social connections outside of the group alive.

Go to your graduate mentor who is present during your meetings. Tell them that you feel like this person specifically ignores you, but that you aren't sure if your impression is accurate. Ask them if they have also observed that, or possibly ask if they can pay attention to the interaction between the two of you during the next group meeting and see if they observe the same thing that you have. Then ask them what to do--either if they say they do not observe the same thing, you can talk to them about how you came to your impression and figure out where you went wrong, or if they do observe the same thing then they can tell you what to do about it.