I guess nobody has ready answer to this, but if I have made God a promise, and it takes some days to fulfill it and pretty much work, what should I do on sunday? I should fulfill my promise quickly, but also avoid working on sunday and keep that day holy to God. Old days it was a sin to do any kind of work on sunday.... and christians were not supposed to show bad example of sunday working to other, not so christian people... so which is more important? Should I anyway go to church on sunday, even if my promise is not yet fulfilled and I should not fulfill it slowly (according the Bible)?
Welcome to CC, Anamaria...
As another has noted, your dilemma is rooted in a misunderstanding of the Bible and its contents.
First, Sunday is not "Sabbath". They are related, but not the same thing. You aren't sinning by working on Sunday. However, you need rest from work, and worshiping God corporately is good for you. If you are able to attend a Christian service of worship, do so.
Second, you haven't explained your "promise" in detail, but it sounds like a financial promise. God knows your physical and financial capacity. Even a financial promise made to God intended to be fulfilled "as soon as possible" doesn't mean that you work 24/7 until you have it paid.
Third, don't stress over what others think, until you have settled what God thinks.
Go to church. Fulfill your promise as soon as you
reasonably can do so. Next time, don't make promises to God that put you in this situation.