The Rega spindles were a little short to begin with. If the new platter is thicker than the original platter, then yes, you will be left with virtually no spindle sticking up. If the record can centered and you're not going to use a clamp, it should not be a problem.
Congrats on your new platter. Are you still using the felt mat on top? Try removing the felt mat and see if you like the sound. YMMV
Congrats on your new platter. Are you still using the felt mat on top? Try removing the felt mat and see if you like the sound. YMMV