Problems with graph plotting looks awkward

I am adding data points onto a plotted graph and adding a trend line y=mx+b equation taken from Excel.

However, the output looks ugly and I am not sure why.

The trend line just stops, the maximum number on the y-axis is missing, and when this prints, the light coloured grid appears dull or not appear at all. Another issue is Case 2 at 60 Ohms will be next part of the data points, but I am going on a tangent here, formatting the three additional tables/graphs I can figure out later on when I get the graph looking correct.

Essentially, any suggestions in making this look more ideal if that means prettier or better is appreciated.

\documentclass{article}

\usepackage[letterpaper, portrait, margin=2cm]{geometry}
\usepackage{pgfplots}
\usepackage{booktabs}

\begin{document}
\section{Results}
\noindent
\begin{tabular}{@{}cc@{}}
\begin{tikzpicture}[baseline=(current bounding box.center)]
\begin{axis}[
title={Case 1 at 40 $\Omega$},
xlabel={Electric Current (mA)},
ylabel={Electric Potential (V)},
xmin=0, xmax=50,
grid=both,
grid style={line width=.1pt, draw=gray!10},
major grid style={line width=.2pt,draw=gray!70},
minor tick num=5,
legend pos=north west,
ymajorgrids=true,
xmajorgrids=true,
yminorgrids=true,
xminorgrids=true,
grid style=dashed
]

coordinates {
(15.61,0.598)
(23.99,0.924)
(30.30,1.173)
(44.70,1.718)
(14.55,0.561)
(16.66,0.642)
(46.80,1.799)
(143.6,5.555)
(28.22,1.086)
(18.19,0.701)
};
\addplot[no marks, thick, color=red] {0.0383*x - 0.0041 };
\end{axis}
\end{tikzpicture}

\begin{tabular}{c c c}
\toprule[1.5pt]
{\bf Electric Current (mA) } & {\bf Electric Potential (V)} \\
\midrule
15.61 & 0.598 \\
\midrule
23.99 & 0.924 \\
\midrule
30.30 & 1.173 \\
\midrule
44.70 & 1.718 \\
\midrule
14.55 & 0.561 \\
\midrule
16.66 & 0.642 \\
\midrule
46.80 & 1.799 \\
\midrule
143.6 & 5.555 \\
\midrule
28.22 & 1.086 \\
\midrule
18.19 & 0.701 \\
\bottomrule[1.5pt]
\end{tabular}
\end{tabular}
\end{document}


Make graph prettier ... this is matter of taste. Anyway, see if the following result is acceptable:

In your MWE I add domain for trend line, define ymin and ymax, add missing & in table, simplify grids style definitions, redesign table:

\documentclass{article}

\usepackage[letterpaper, portrait, margin=2cm]{geometry}
\usepackage{pgfplots}
\usepackage{booktabs}

\begin{document}
\section{Results}
\begin{center}
\begin{tikzpicture}[baseline=(current bounding box.center)]
\begin{axis}[
title={Case 1 at 40 $\Omega$},
xlabel={Electric Current (mA)},
ylabel={Electric Potential (V)},
xmin=0, xmax=50,
grid=both,
grid style={line width=.1pt, draw=gray!50},
major grid style={line width=.2pt,draw=gray},
minor tick num=5,
legend pos=north west,
%ymajorgrids=true,
%xmajorgrids=true,
grid=both,
%minorgrid,
%xminorgrids=true,
grid style=dashed
]
coordinates {
(15.61,0.598)
(23.99,0.924)
(30.30,1.173)
(44.70,1.718)
(14.55,0.561)
(16.66,0.642)
(46.80,1.799)
(143.6,5.555)
(28.22,1.086)
(18.19,0.701)
};
\addplot[no marks, thick, color=red, domain=0:50] {0.0383*x - 0.0041};
\end{axis}
\end{tikzpicture}
&
\begin{tabular}{c c}
\toprule
\textbf{Electric}       & \textbf{Electric}         \\
\textbf{Current (mA)}   & \textbf{Potential (V)}    \\
\midrule
15.61 & 0.598 \\
23.99 & 0.924 \\
30.30 & 1.173 \\
44.70 & 1.718 \\
14.55 & 0.561 \\
16.66 & 0.642 \\