You describe your first option as "Norwegian with Swedish mixed in". Given the language proficiency you describe, I think that a better description of your options would be to speak plain Swedish or to speak Swedish with a few Norwegian words mixed in. What I mean is that, since you know Swedish much better than Norwegian, what you say will likely be interpreted as Swedish either way. The few specifically Norwegian words that you may know and use will have much less weight when they subconsciously determine which language you are speaking than the specifically Swedish words and expression you cannot avoid using. On top of this your pronunciation/accent is likely to sound more Swedish than Norwegian no matter how hard you try. The thing is that a Swedish person will probably notice the Norwegian flavor that you may add to your Swedish, but to a Norwegian the Swedish flavor will still dominate their impression. People pay more attention to the things that doesn't fit with the language that they know well and speak themselves.

As a native Swede living in Sweden, I know several Norwegians who have lived in Sweden for many years. I know that they have adapted their vocabulary and and pronunciation quite a lot and that they would probably consider themselves to be speaking Swedish. Still I know that I and other Swedes instinctively perceive them as speaking Norwegian. I also know Swedish people who have lived in Norway for a long time and experienced the reversed situation.

That being said, I would recommend mixing in Norwegian words and expressions as you learn them. It will make it slightly easier for them to understand you and it will make you more comfortable speaking with Norwegians in the long run. Either way they are likely to think of you as speaking Swedish, but unlikely to find it rude. If someone would actually find it rude, it's unlikely that there is anything you could have done differently to avoid it.