Hello Christine.
I have some experience with horse manure (experience is the name that we give to our mistakes!).
Not to worry that the horse manure might be, or seem, a little fresh, or has sawdust in it.
For next time, try to make a cubic pile(s), about 1m (high) x 1m (wide) x however many metres long you can manage (at least 1m long).
Make sure that the horse manure/sawdust mixture is well watered.
I suggesting a gentle garden hose mist as you are stacking the manure in your bin(s).
After 24, 36 hours there will probably be a large increase in temperature.
Try to get the temperature above 45 degrees (C), and better still, above 50 degrees (C).
After a few days you will notice the volume (height) of the pile shrinking, and the temperature falling.
Depending on available muscle power and time, you should aim to toss the pile into a new bin after 3 or 4 weeks. (After 2 weeks is slightly preferable, but this is a trade off between time/muscle power available, and other garden priorities.)
After the toss (and very slight misting) wait another 2 or 3 weeks. The temperature, initially, will probably rise again, though probably not as high as the first time.
If you have the patience and the time, wait for a few months before using the manure.
There is probably no need to toss the manure a second time. But if you have the time and energy, this is recommended.
You will notice that the final volume – after 3 months – will probably be about 40% of the original volume, because of compaction, and oxidation of the original material.
I hope this helps.