Not calculating correctly

For the last week my watch has not been calculating steps nor distance correctly. i have been doing the same Park route which is .62 of a mile and each day I’m done the distance isn’t correct. different reads have been .4, .41, 1.24,etc.  I run/walk at least 3-5 laps, each being .62 of a mile. my steps have looked about right one or 2 days but the others only show 300 steps, 150, etc. the majority of the time incorrect as well. I haven’t had this watch for more than a month. Purchased on amazon. how do I go about getting a new watch that doesn’t have these errors? Thank you!