no
you have to explain why we can't be sure of our ultimate fate
if
we choose to follow Jesus
I know that some who oppose openness theology say that it amounts to the same thing because only a few get to be saved whichever way you look at it.
In a way I agree but open theism is so much tastier. Not all biscuits are the same.
Calvinist biscuits taste bad and look awful. A lot of people find them hard to swallow. Catholic biscuits taste bland but they are nicely decorated, which makes them popular, especially amongst folk who don't really care much about what they are eating. Openness biscuits taste great and are averagely decorated.
In openness you are as sure as is reasonable to be about your eternal destiny. In Calvinism you are not sure at all. Or rather one half of you is sure and the other half of you is petrified in case you aren't saved at all. In Catholicism, you aren't all that sure but you also aren't all that bothered because you have purgatory to fall back on.
In openness you are as sure as you can reasonably be because you are free to reject God if you really want to but otherwise you know that you are completely secure in the arms of the living God. It's that freedom that gives your salvation its delightful taste.