Alas for the poor ellipsis! He’s completely overused, overworked, and quite rankly far too routinely abused in our 21ˢᵗ century world. Please consider giving him a well deserved break. After all, you don’t see him peppering every page of fine English literature, now you do?
Also, the correct formulation in English for this sort of optative exhortation must begin “If only”: you cannot interpose any words between the If and the only as you did above. For example, one might say If only it were otherwise! and be on perfectly sturdy ground. It just wouldn’t do to insert it were between the first and second words; it ruins the effect and the meaning.
You therefore should have said
If only I had said ‘I love you’!
Although one need not have quotation marks in indirect speech, which this is.
If only I had said [that] I love you!
I’ve used an exclamation point in all these because such exhortations are generally considered formally exclamatory in nature. You can see this in the other common way of saying the strong phrase above: Would that it were otherwise!
There is one exception. Maybe you meant something different. If you actually meant that you wished you had said nothing beyond those three words but instead had said more than that such that you now feel regret at talking too much. Because that’s what your phrasing comes across as saying.
Try it the other way if that was not what you intended. I think you’ll find it works better that way.