Welcome to iRV2 .
Sorry your first post is about problems .
It would appear from your photo that your plastic water pipe is grey and if memory serves the gray pipe takes different fittings that clear pex .
Always best to use the pex cutter for square cut . But you may want to check with the cap supplier to see if they are the correct for your grey pipe.
What year is your RV ? The grey pipe was only in use for a few years in the late 90's.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.