so anxious .my first mistake

hello nurses.iam a student ,actually on the 4th year of the uninersity practicing in a hospital in Greece.my actual "experience" is a month in which I cant say I learnt so many things.to get to the point my mother yesterday asked me to give her an IM injection of apotel (paracetamol and lidocaine)I have to say that my mother is overweight (120kg) and I used 21g approximately 4cm needle and as I saw I accidentally injected it subcutaneously ..as the drug action wasnt as fast as always and she said that during the procedure she felt the drug moving and expanding further.she also refers today pain tenderness lower than the injection point heat and feels like she cannot raise her arm.i ve never had this experience again with some of the patients I had and seriously have no idea what to do.any thoughts?