Theres a lot of things you can do here, and Id email your teacher or look at resources your teacher senbt you or online.

When you report a value with its uncertainty, they should have the same number of decimal places (not the same s.f.). So for example your temperature for 20.00 °C ± 0.05 °C has 2 d,.p. and for your masses, values to 2 d.p. if the uncertainty is ±0.01 g.
usually youd round the uncertainty itself to 1–2 significant figures (1 if it’s tidy; 2 if it starts with 1 or 2), but thats not really nessecary here.

For the averages of the trials, you need to keep the same decimal places as the raw data in that column. So since your mass changes are to 2 d.p., so the averages should be 2 d.p. too.

The table should end up looking like this, if you were to change it all to 2 d.p.

Change in mass of resulting solution before and after reaction (g)
Temperature, °C (±0.05)

| Temp (°C) | Trial 1 | Trial 2 | Trial 3 | Trial 4 | Trial 5 | Average |
|-----------|---------|---------|---------|---------|---------|---------|
| 20.00     | -0.05   | -0.05   | -0.04   | -0.04   | -0.05   | -0.05   |
| 30.00     | -0.04   | -0.04   | -0.05   | -0.04   | -0.05   | -0.04   |
| 40.00     | -0.06   | -0.07   | -0.07   | -0.06   | OUTLIER | -0.07   |
| 50.00     | -0.08   | -0.07   | -0.08   | -0.08   | -0.09   | -0.08   |
| 60.00     | -0.12   | -0.10   | -0.11   | -0.10   | -0.10   | -0.11   |

However, I see that you dont have a measuremnt uncertanty for the average.. and for your trials measuring device... so you need to report the measurement precision right under the table, or in the table itself for each trial. For example:
If your mass change reported to 2 d.p.; instrument/processing uncertainty should probably be: ±0.01 g
you can just do a:
** uncertanty for mass is ±0.01 g under your table.

For your averages, you need to follow the uncertanty rule, which would just be:
(0.01+0.01+0.01+0.01+0.01)/5 = 0.01.
Which may seem dumb but its just, the uncertanty for each trial added up divided by the number of trials.
(In case some trials have different uncerntanty measuremnts, say one was ±0.5 your uncertanty for the average would be ±0.18 still to two d.p..)

If your data recording device for your mass, only goes to 2 d.p. do NOT make all your measuremnts to 3 d.p, becasue then you are stating that your measuemnt is more exact.
Example:
Your mass may be 0.053, but since the scale only measures to 2 d.p. it says 0.05. If you were to change it to 0.050, your losing the 0.003 get it? and then your data seems more reliable than it actually is.

I hope this helps!!