Uneven Platter Problem

I use a budget, belt-driven Gemini TT-01 turntable. It's not great, but it spins the wax...kind of. I've noticed that as the platter spins, it has a slow rhythmic "up-and-down" on one side. It's almost as if one part of the platter is slightly higher.

I've checked the belt to make sure it's even and the table itself is also even. How do I fix this?
Cheap tables commonly have a bit of "swim". Take off the mat and observe the naked platter, if it does not swim, there is some eccentricity in the mat, sometimes just repositioning it on the platter can help. If the platter iteself swims, gently, gently, try to rock it around the bearing. If it moves, there is play in the bearing, also common on inexpensive decks, and the spindle is just moving around in the bearing housing, not much you can do about it and it is probably not the worst thing in the world. If it bothers you, hang out in the Goodwill stores and buy yourself a good, older direct-drive. Technics, Kenwood, Pioneer, they all made them and Goodwill has them for $25.00 and under. Most are excellent performers with very little eccentricity in the platter. Lots of eccentricity in the Goodwill employees though.
Yeah, it's definitely the platter. I can push it down and move it around a little, kind of like it's meant to have a little give in every direction. Is there any way to fix it? It was a gift from my girlfriend, so I have to at least keep it a little while before I move on.
No need to fix it, or give up the little lady; it is operating well within its manufacturing tolerances. This is pretty common, I do not know for sure, as I have not seen the table in question, but I'm a bettin' man and will bet that, if you looked at a dozen of those Gemini tables, all of them would have some swim to the platter. It really is not hurting anything, other than adding a bit of wow, which you have not complained about. Just enjoy the damn thing and be glad that you have a girlfriend that wants to support your interests.
I'm definitely glad about having a wonderful girlfriend supportive of my audio interest! And I do notice some wow in the sustain from piano and guitar. I just got the Shure M97xE which has a dynamic stabilizer brush that is said to help this a little.
Nice choice of phono cartridge, when you upgrade to a better table, you will be able to use it on that. It is also very good with the lighter arms that are common on less expensive tables. BTW, now that you have your girlfriend on board supporting your interests, you now only need to get her a job that pays a lot more money so that she can buy you that VPI table and arm that you've had your eye on.