I think [name_f]Lottie[/name_f] works very well as a standalone name. I know an adult [name_f]Lottie[/name_f] (early 30s) who I think is legally [name_f]Charlotte[/name_f] but who I’ve literally never heard called by anything other than [name_f]Lottie[/name_f] in over ten years, including professionally. I think it will be fine.
I was going to suggest [name_f]Lotte[/name_f] and I see above that you like that too, but I do think in the US pronunciation would be a problem.
I think it’s fine as a stand-alone. [name_f]My[/name_f] only issue personally, as someone from the UK, would be that the ‘nicknames/diminutives as stand-alones’ thing is a definite trend, and trends date. This may not be something that’s relevant where you live, or even if it becomes relevant, it may not bother you.
The flip side of that consideration is what is the point of naming a child something you like less just to get the nickname you adore. Why not just give the name you love in its own right. You’ve already experienced this and didn’t bring you satisfaction, so it would be madness to repeat the same mistake.
[name_f]My[/name_f] advice to you would be, if this is the name you both truly love, then go for it. 
[name_f]Lottie[/name_f] [name_u]June[/name_u] is so cute! I think it can work as a name on its own to be honest. If you’re nervous about it I’d say choose [name_f]Charlotte[/name_f] so she can go by [name_f]Lottie[/name_f], and then if she wants to change it up when she’s older, she has many other options. Otherwise, [name_f]Lottie[/name_f] is good. I’d go for it. Good luck.
I think it works as a standalone name. [name_f]Lottie[/name_f] [name_u]June[/name_u] is adorable!
[name_f]Lottie[/name_f] [name_u]June[/name_u] is beautiful!!! 
Lottie works perfectly on its own! Right now nickname-y names are trending and Lottie fits right in. Lottie June is perfect!
I like how Lotte looks, but I do think in the US most people will assume it’s pronounced lot. In my opinion it would be best to go with Lottie to avoid having to constantly correct pronunciation and spelling. It’s a beautiful name either way though, good luck!
I’m actually thrilled to see someone considering [name_f]Lottie[/name_f] as a standalone. The only reason I ever had [name_f]Charlotte[/name_f] on my list was as a way to get to [name_f]Lotte[/name_f].
I have considered [name_f]Lottie[/name_f] as a stand-alone name myself, so I totally think it works! I think it was used a stand-alone name a long time ago. It is well known enough to be a name of its own.
I’m with you on not like the longer forms, I just like [name_f]Lottie[/name_f]. And [name_f]Lottie[/name_f] [name_u]June[/name_u] is absolutely precious!
Congrats and I say go for it!
I think [name_f]Lottie[/name_f] is perfect as a stand-alone name.