The match has been going on for quite a long time and currently Stuttgart is still leading 1-0 against Union Berlin. It looks like your worries are confirmed because Union Berlin is still not capable enough to stop Stuttgart. I think if Stuttgart can score 1 or 2 more goals then victory at home is guaranteed. But if Stuttgart is careless then they have to be prepared for the worst possible result of a draw.
Stuttgart continues its good performance in the last 5 matches. The victory they just got from Berlin means that they will still remain in third place in the Bundesliga with an insignificant points gap with Bayern Munich.
In fact, Union Berlin actually could match it, but they received a red card in the second half. So they were unable to make up for their losses. Yes, even though in fact, after the red card, Stuttgart couldn't add any more goals. However, the 2 winning goals were very satisfying for them.