Ecclesiastes 5 v 5: It is better not to vow than to vow and not pay.
Prov 6 v 1 -4: My son, if you become surety for your friend, if you have shaken hands in pledge for a stranger, you are snared by the words of your own mouth; You are taken by the words of your mouth. So do this, my son, and deliver yourself; for you have come into the hand of your friend: Go and humble yourself; plead with your friend. Give no sleep to your eyes, nor slumber to your eyelids.
That is why the scripture in Proverbs above is so awesome. God says, if you feel you can't do it, go to the person involved and un-commit yourself! Go with humility. Be honest. Pray first for God to soften their hearts and for them to be understanding. The relief you will feel is amazing. If you feel relief then you know you did the right thing. If you feel condemnation, then thats the devil messing with your mind. But if you feel conviction, then maybe you should have pushed through. Check your motives, make sure you want to undo your commitment for the right reasons.
As it says in Ecclesiastes above, to paraphrase, 'its better to not offer help than to offer help and let that person down because you can't do as you said you would'. The thing I have taken from this is to make sure when I commit to something, I am willing to sacrifice the time and effort and that I will do it as unto the Lord. But if I feel guilted into it, then I know, dont commit to this; 'My attitude will be wrong and I'm likely to let these people down'.
I encourage you to pray and think about any commitment before taking it on. I believe the closer we get to the Lord the more He uses our consciences, so if you feel peace about something after praying then move on it. If not, then don't. As the old saying goes, 'when in doubt, leave out'.