unique situation perhaps?

Hello fellow canucks!

I have somewhat of a unique situation. I am a Canadian citizen and resident of BC. This past summer I did an internship at a registered non-profit organization in the states for 10 weeks. I have since returned and was granted a 6 month visitation under a B2. Some of the border officers weren't thrilled that I was planning to stay 6 months considering I was there already for 2 1/2 months a month before that. I'm afraid that if I go back I may not be allowed in for some time. What is the best option, if any, to remain and volunteer longer? Is there a visa I could transition to while I'm here besides an F1? I've heard that applying for a B2 extension as a Canadian citizen is useless. Any feedback would be great.this is such a confusing process for me!

What sort of non-profit is it? Is it a religious organization?

I think there is some sort of religious worker/volunteer/missionary visa, but I don't know much about it, or how to be eligible.

Hey thanks for the reply!

The organization I've been helping out is a registered non-profit geared towards rare plant conservation. I haven't found a visa that resembles this at all. if anyone knows of anything please let me know! Much obliged