You have the right size as in 35mm=standard. Did you prime the inside cap and carto with some juice? Even with priming it takes some wiggling and elbow grease to get that sucker on. It'll get easier but it is tight!
Ps. Do you have a carto fill tool? This will help keep the sharp edges of the carto from cutting into your inner cap rings. I got mine at IBCtanked for like $2.50. You can put that on to keep the carto's edges smooth while working that endcap on. Just keep working the edges of that cap down and around.
That happens with the Phiniac, the juice running out the bottom. I don't know why. Just clean it up and it should vape like a champ! I never have to prime my carto's prior to vaping them because the Phiniac seems to do it for you. Weird. When I mentioned priming the carto in my previous post I meant the outside, sorry about the confusion I shoulda been clearer.
I have never had the juice run out of the carto using a Phiniac tank and I fully fill my cartos before putting them in the tank.
If it keeps leaking out the bottom it could mean you cut the oring/s trying to insert the carto. If the oring/s get damaged the tank won't seal properly and the juice will run out the bottom of the carto. That's why it's a good idea to use the tank tool when inserting cartos in a Phiniac tank.
If it does keep leaking you will need to replace the inner orings and all will be well.