do not give it any nutes..plenty of nutes in the mg soil for a couple more weeks....it will be fine.... perfectly normal for a young plant to get slightly burned tips from the mg soil...relax and enjoy watching her grow
is that a foam coffee cup? ...if it is i would let the soil dry and put it in a plastic cup...the foam cups seem to grab hold of the roots and you will not get a clean transfer when you pot the plant