You must had double clutched to go back in 1st. usually sycronizers dont allow that easily.
there is no harm, if you need to do that, double cultch and push throttle up to match rpm speed. but it will not be effective acceleration on a frontwheel drive cars, result in stupid wheelspin.
Once i raced ae86 with mr2 turbo in 1993. , we were at rolling, the mr2 guy goofed me by going back in first to fully use full rpm.