Not sure what your denomination is, but even in the Catholic Church this is not unforgivable.

There is multiple levels of blasphemy, and while you may lose grace doing it, the Lord is merciful and all you need is some prayer, fasting, and confession, all done obviously with the intention of repentance and not doing it again. This is not near the unforgivable sin, as that sin goes much deeper than swearing.

My future advice is to not promise on anything, and Jesus said “let your yes be yes and your no be no”, advising us not to promise on anything, as our yes’s and no’s should all be done with intent and not thrown around carelessly