Hey. You can’t swap and change embeddings I’m afraid. Bear in mind that embeddings are just (a part of) model weights. So in order to compare your short sentence, you need to compare it with weights from the same model.
AFAIK, document vectors can be arrived at in a couple of different ways. It may be that you can just generate document vectors for your short text, but I’m not sure TBH. If it’s gensim doc2vec then try this:
https://groups.google.com/forum/m/#!topic/gensim/Fujja7aOH6E