If your paper isn't in the proceedings it will be difficult for people to cite your work, or even to know the details unless they happen to be among the few that attend your presentation. As to your questions:
What it means should be explored with the conference committee. Probably it means that only the title will appear.
Yes you can put it in your CV as long as you list it properly as one that was "presented at ..."
Yes, it won't hurt you in grad school applications and will probably help, though a paper that is formally published would be better. People will be looking for evidence that you will be successful in academia and this is a positive thing, even if it doesn't appear.
Maybe it would be better to try another venue, but there is risk in that. It might not be accepted and even if it is, it might not be accepted in time to show up in your grad school applications.
You might ask a trusted advisor for advice, and should certainly explore it a bit with the conference committee. Perhaps you can present it here and publish a complete version elsewhere. It would be very odd if they expect you to give up rights under these circumstances. If they do ask for copyright it would seem to me to be a red flag.
Also, at the point you are in your career the effect will be small overall. Any research line in your CV is a good line when you are an undergraduate.