There are a lot of different ways to do a make 1 increase, so I'm not sure what's going wrong here. But I know that when I do a make one, if I don't knit into the back
of the stitch I just made, I will end up with a hole.
Also, some types of make 1s do produce a small hole, so it may be that you aren't doing anything wrong.
There are a lot of videos here that tell you how to do various make 1s.