You probably just need to start over and make sure that you comply with all court rules and standing orders. My strong advice would be to hire an attorney to file this correctly on your behalf.
The rules for Standing Order 2-99 are very strict. You can read the rule here:
http://lawlib.state.ma.us/source/mass/rules/probate/standingorders/2-99.html. It is important to note that you are not allowed to schedule the matter for hearing. The Motion is determined on the pleadings alone.
If the window has passed, you may still be able to file under Rule 60: http://www.lawlib.state.ma.us/source/mass/rules/civil/mrcp60.html
You should consult and/or hire an attorney to remedy the situation as it is clear there are certain rules and procedures that need to be filed.
This response is for informational purposes only and not intended to be legal advice; nor is this answer intended to create an attorney/client relationship. Legal advice and an attorney/client relationship can only be rendered after a full in person consultation has been conducted with an attorney wherein all necessary facts and circumstances are disclosed. To the extent additional or different facts exist, the within response may be different.
I think you are misreading the 10-day deadline. The 10-day deadline applies to your opponent serving an opposition to your motion. The deadline for you serving and filing the motion itself is not governed by the Standing Order (2-99), but is governed by other rules, such as Rule of Domestic Relations Procedure 60(b), etc. So your deadline may not have passed as you think. However, the clock is ticking, so you should consult with an experienced Massachusetts family law attorney right away. Otherwise, you may be barred for three years from seeking a modification of the support amount.