My 3 year old isn’t taking the antibiotics

Hello all, my 3 year temp was so high like 40 so we went a&e dr checked him over and said he’s fine but didn’t know why he has a high temp so he gave us cefalexin antibiotics, however it’s been a mission and a half to give it him now he’s refusing to eat or drink anything as he thinks it in it, his temp has been down since morning it’s 36.6 now, it was. 3 day cours has anyone stopped sooner and has ur child been ok? Reading on google is scaring me saying u can be more worse off, as an adult I never completed the course of antibiotics and I’ve been totally fine.