So, my boat sets deeper in the water in the back with all the weight. 90 hp merc and two talons. Should the transducer be angled up when sitting on the trailer, so it is more level when boat is in the water?

yes if it is a side/down image ducer, standard sonar is not as picky

I agree with hopalong. For a traditional sonar transducer, keep in mind that some forward angle is desirable. That small tilt forward (for the beam, meaning the transducer body is tilted aft) is helpful to not outrun your sonar return pings. As you speed up on plane, the boat moves more substantially forward after any given ping is transmitted such that the transducer is in a different spot when the "ping" gets back to the surface after bouncing off the bottom of the lake. Tilting the beam helps to accommodate this characteristic.

Most transducer installation instructions will suggest some amount of tilt. Numerous boats have a transducer inside the bilge area, so those are already tilted by the angle of the bottom of the boat at the transom. The best starting point is usually parallel with the bottom of the boat, which gives you a bit of that forward beam angle. It will have a negligible impact on depth reading as the beam is typically 20 degrees wide anyway.

More important to actual depth accuracy is the offset setting in your sonar unit. Since the transducer is not at the surface it's not measuring from the surface. The offset setting is how deep into the water your transducer is sitting when it matters most to you. That setting will build in a correction to give a true depth reading.