You should start by aiming the heat bulb over by the ramp, and then if you see then basking up there(if could take over 5 days for them to get used to it), you can slowly, a little bit a day, move the heat back to where you want them to bask, and that should draw them back to where you want them to bask.
If you don't see them up there, then you need to make the ramp longer, with more traction, and maybe a less steep angle. You could use a piece of plexieglass, with something on it for traction.
If you use un-sealed plywood if will leach all kinds of stuff into the water. But if you have to use it, and have no other choice, then you can seal it(like the hull of a boat) so that it is water proof. Or you could even try getting the large size zoo-med basking platform.
Good Luck!!!

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RES's
Tank, SCL 3.75in.
Diesel, SCL 3in.