I have a 3 wire circuit, and the neutral has 13 amps reading on it, is this normal?

Sounds either like only one circuit has a 13 amp load, which is fine. If not and there is current on both that add up to 13 amps, then each circuit is on the same hot leg in the panel, and one needs to be relocated to the opposite hot leg.

The Neutral Current shoud be the difference of both hots.
If 1 circuit draws 10 amps and other circuit draws 12 amps then Neutral shoud be carrying
2 amps. If Neutral is carrying total of the 2 hots, then like Tk says, needs to be on opposite phase.