I have uneven nipples and no underboob. Is it fixable? (Photo)

I do not think it is realistic for you to get or expect a 600-700cc breast implant in one surgery.  I also do not think that this size implant will fit your frame because it will be far too wide for your frame.  I agree with my colleague, that you do have a constricted lower pole of the breast which means there is "less skin" on the bottom of the breast and this takes time to stretch out with an implant and can only do so much at any one time.  Sometimes this have to be done in two surgeries. The skin can only "stretch" so much at any one time or surgery. The nipple/areolar "diameter" can be "adjusted" at the time of the surgery as well. I hope this helps.  Good luck!

From the photos - You have a moderate tuberous breast deformity.  This occurs when patients have a constricted, or tight lower breast pole (or as you stated "lack underboob").  Breast augmentation surgery with surgical release and scoring of the inferior pole constriction allows the implant to better fill the inferior pole during tuberous breast correction.  Some patients benefit from an areolar reduction as well.  See an ABPS board certified plastic surgeon for a full consultation prior to surgery.