I had a temp Illeostomy in April and have had it takendown since then. When I had it I had a lot of trouble with pouch not sticking. My Illeostomy nurse finally tried the stick paste, it worked wonders, also try a convex appliance and see if that works.
To use the stick paste take it and gently put it around the opening ( do not stretch or handle anymore than nessary)
then put appliance over it and hold down a min or two.then put pouch on.
Hope this helps you as much as it did me, I had no more leaking and bag stayrd on 3-4 days.