To spank or not to spank?

So tonight my 4 year old son refused to take his snow covered boots off, I sat him down and began removing them and he kicked me so hard in the face, I proceeded to slightly tap his bottom(he was wearing windbreaker pants that were all wet from snow play) the sound was loud but he never cried until he saw his boots off, I never spank him ever I just don't see the point but he kicked me so hard! My mother who was in her room freaked out started yelling saying I'm beating him and I am a horrible mother and all this! I am so upset, I may have reacted and spanked him but in my eyes he has to learn not to kick me! I feel so bad, I know it didn't even hurt, there was no mark at all and with all the padding he had on there is no way it even stung! :( idk if I was wrong or not ... I know people are against spanking and I sort of am, unless he causes me physical pain I never hit him and when I say hit I mean tap like barley feel it the only thing that gets hurt are his feelings , any help for me would be appreciated....  I forgot to add my mother plans to call cps because of this, I can't even sleep I am worried sick and I know I didn't even do anything wrong!!!  :( fml