Would this make keeping the Sabbath on Sunday wrong or sinful?
Insofar as we define sin as "missing the mark" (the literal translation of both the Greek and Hebrew word), yes: It misses the mark of correct Biblical understanding.
Fortunately, it's not the unforgiveable sin, and we are saved by God's grace, received in trusting Yeshua the Messiah, not by keeping all of God's Appointed Times in just such-and-such a way. I don't generally make it an issue except with two groups of Christians:
1) Those who want to rag on me for supposedly following rabbinical traditions instead of the Bible--my point to them is that if they're going to follow church tradition where it does conflict with Scripture, they shouldn't hassel me about following Jewish traditions in instances where they don't.
2) Those claiming that their denominations traditions are the original apostolic church, e.g., Roman Catholics and Eastern Orthodox. My point to them is that a) God rates obedience over lineage, and b) the Apostles were Torah-observant Jews (cf. Acts 21:20ff), not Roman Catholics.
To which she followed up by asking, Do you mind telling me how you keep it? That is, do you keep it more or less in the manner it was kept during the time of Jesus?
Oh, most certainly not!
Understand, at the time of Yeshua, the rabbis had added so many rules to define just what constituted "work" that they had literally turned not working into a heavy burden. It was so bad that when Yeshua miraculously healed people on the Sabbath, they accused Him of sinning!
I have no desire to return to that.
I strive to keep Sabbath after the simplicity taught by our Lord. I never do overtime on the Sabbath (thankfully, God has given me a job where I can control my hours), nor do I try to catch up on any of my chores around the house. Laundry can wait another day. :)
I go to synagogue, i.e. church. Since God has not granted that I live close by, that means about a 20-30 minute drive. That would definitely be frowned upon by the Orthodox, but in this case, I have to go by the Lord's take that "it is lawful to do good on the Sabbath."
Thus, when I preach in prison or teach the youth group on the Sabbath, even if it means being on the road for 30-90 minutes, I don't see myself violating God's command any more than a priest ministering in the Temple (Mat. 12:5) or a rabbi circumcising a child (John 7:22).
Other than that, I relax, I read, I visit with friends. I'll occassionally chat with friends on FR and elsewhere online, but I make it a general rule not to let debates carry over into the Sabbath; they too can wait another day.
Yeshua teaches us that, "The Sabbath came into being for man's sake, and not man for the sabbath's sake" (Mark 2:27). That is, the Sabbath, a day to set apart from the pace of the rest of the week, a day to sleep in, to relax, and to be with God and your family and friends, is a blessing, not a burdensome religious duty.