It should have been done with a bathroom caulk and the gap should have
been about 1/8 inch. Caulk remains flexible so that when the tub has
the weight of water in it, it will flex and not crack. It should be
done with the tub near full and allowed to cure, as that will have the
space at it's widest. If there is enough room, you can go over the
grout with caulk, or else remove it.