overly, overlie, overlay

Overly or overly means excessively; too--
He tends to be overly precise; this job will take him all day.
You may think we're being overly cautious, but the danger is real.

Overlie or overlie means to be spread over or upon, as a layer or stratum--
This granite will overlie the front steps of the building.
A layer of sediment will overlie the rocks at this time of year.

Overlay or overlay  means to spread or put over, as a sheet of paper or a coating of a decorative substance--
He plans to overlay the entire piece with gold leaf.
Overlay may also mean a layer, or a transparent sheet placed over a photo or map, either blank or with additional information--
Changes in the map will be noted with an overlay.

Now that you know that, you can say--
"An overlay of marble will overlie the pedestal; we hope it won't seem overly ornate."

Note--"layover" ( one word ) means a wait between connecting flights--
We will have a two-hour layover in Chicago.
Note # 2--"lay over" ( two words ) means to be placed or spread ( lay ) on top of ( over )--
The towel should lay over the railing, so it will dry.

overly, overtly

Overly or overly means excessively; too--
He is often overly cautious; he won't try any thing new.
The manager can be overly exacting, but he pays us well.

Overtly or overtly means openly or publicly--
He was overtly hostile; there wasn't anything subtle about it.
He made the offer overtly; everyone knew about it.

Now that you know that, you can say--
"He is overtly ambitious, and not overly sensitive to the opinions of his coworkers."

Note--"overlie" means to be over or upon, as covering or stratum--
A mat of leaves overlie the wildflower seedlings you are looking for.