You do not have to push
The wording on Repelling Blast is as follows:
When you hit a creature with eldritch explosionyou can push
the creature up to 10 feet from you in a straight line.
— Player's manualp. 111
the can Here works as an option, which means you are free not to do it. If this word had been omitted, you would have no choice but it is there.