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It is, but Christians based their morality on a higher being. I been to bible study sessions before, and I had to interpret archaic messages and scriptures, to which I found to be a very difficult endeavor. 
It might just be a "me" problem since I was never adept at literary analysis. 
The secular humanist's moral framework seems to be very straightforward: do good acts for self-fulfillment, not to appease a higher power.
Why only these two choices? Sikhism also has a great tradition of charity and humanism. >

Sikhism isn't too big from where I am located. I thought about Buddhism for a bit, but I ultimately decided on becoming a secular humanist. >

Fair, but why is becoming a Christian in the mix? It sounds like you've made a decision.
I would argue that you're still free to take inspiration from Christianity, but then it sounds like you're interested in the world (hence your research into Buddhism and Sikhism), so why is it necessary to pick a religion? I'm sure Christians would welcome you either way if your intention is to help people, no?