As long as you performed your preparations thoroughly earlier that day and inspected your body carefully for barriers prior to your immersion, you can presume that your immersion was valid. Especially in this case where you are not certain whether there was anything on your foot, and that sensation could simply have been the water itself gliding over your foot. Further, even if only one immersion out of three was valid, you still are tehorah.
In sum, do not worry about your tevilah, it was fine. Try not to dwell on these lingering doubts. Once you have immersed, you should focus your mental energies elsewhere (your relationship with your husband, etc.) and try not to think about your immersion anymore.
B'Hatzlachah!