I took some vows long before I was Hindu that I shouldn’t have made. Are these vows valid since I didn’t have a witness?
No vow can be taken without any witness. There are universal forces, apart from our own soul itself, which are always the witnesses.
See the following verses from Manu Smriti:
8.84. ’The Soul itself is the witness of the Soul, and the Soul is the refuge of the Soul; despise not thy own Soul, the supreme witness of men.
8.85. ’The wicked, indeed, say in their hearts, "Nobody sees us;" but the gods distinctly see them and the male within their own breasts.
8.86. ’The sky, the earth, the waters, (the male in) the heart, the moon, the sun, the fire, Yama and the wind, the night, the two twilights, and justice know the conduct of all corporeal beings.’
So, there are always many witnesses for any such vow which have been taken. And, vows are usually meant to be kept and not broken.
People usually tend to think in the manner like it is mentioned in 8.85 that there are nobody around us, so we (or our certain acts) have gone unnoticed. But that's not the case. In the spiritual realm, there are many witnesses.