Being able to bring up specific past examples (rather than general ideas) of things you've accomplished, patients you've assessed/treated, etc., is actually something that'll come in quite handy once you get around to interviewing for jobs, so getting additional practice with it now is a good thing. Honestly, I'd say one of the most important things you can do during interviews is to genuinely sound excited. If you have two applicants who say the exact same thing, but one does it with energy and enthusiasm while the other is fairly subdued, odds are most places will rank the first person just a tiiiiny bit higher. This isn't universal, of course, but I've certainly seen it play into ranking decisions.
Try not to worry about the "blabber," either. If you go through another mock interview or two, let yourself run wild, and then let the interviewer tell you if they thought you essentially talked too much.
And always have in the back of your head a small handful of things (maybe 4-6) about yourself, your training, and your goals that you really want these sites (or, in the future, potential employers) to know about you. During interviews, find ways to tie their questions and your subsequent answers back to these points. During my internship interviews, for example, I felt that my breadth of training experiences and patient populations with whom I'd worked was an advantage, as was the fact that I was often the only neuropsych person in the area, so I worked these points into my answers as much as was possible, while also tying it all in to the types of rotations and patients I'd likely be able to see at each site that would help round out my training.
