You are using the wrong fitting, get the right fitting and the hose will slip on with little difficulty. Do not use 90^ fittings for waste hose, Murphy will visit you at the worst time.
The fitting should NOT have any barbs in them they are smooth and while snug do NOT require expand, heat, boiling water to make up.
This is not something to screw up in a hurry, you don't want to go back and re-due in your lifetime, do it right.
Buy PVC adapters to make up a fitting if you cant use over the counter fittings.